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Plate Tectonics: Diverging, Converging, and Transform Boundaries
NSDL National Science Digital Library
In this lesson, students will learn to distinguish the different layers of the Earth, observe the effects of plate movements, and explore the reasons for earthquakes and volcanoes. They will label and measure the thicknesses of each layer of the Earth (lithosphere, asthenosphere, etc.) and record their results, construct models from sand and clay to illustrate what happens at the three types of plate boundaries (transform, diverging, and converging), and investigate convergent plate boundaries to see which scenarios may create earthquakes and/or volcanoes.
Composite transform-convergent plate boundaries: description and discussion
The leading edge of the overriding plate at an obliquely convergent boundary is commonly sliced by a system of strike-slip faults. This fault system is often structurally complex, and may show correspondingly uneven strain effects, with great vertical and translational shifts of the component blocks of the fault system. The stress pattern and strain effects vary along the length of the system and change through time. These margins are considered to be composite transform-convergent (CTC) plate boundaries. Examples are given of structures formed along three CTC boundaries: the Aleutian Ridge, the Solomon Islands, and the Philippines. The dynamism of the fault system along a CTC boundary can enhance vertical tectonism and basin formation. This concept provides a framework for the evaluation of petroleum resources related to basin formation, and mineral exploration related to igneous activity associated with transtensional processes. ?? 1992.
Ryan, H. F.; Coleman, P. J.
Analogue models of obliquely convergent continental plate boundaries
NASA Astrophysics Data System (ADS)
Analogue models are used to examine crustal-scale faulting at obliquely convergent continental plate boundaries. A uniform Coulomb material is deformed with basal kinematic boundary conditions to model two obliquely convergent lithospheric plates. The mantle part of one plate is assumed to detach from its overriding crust and then be subducted beneath the other plate. The obliquity of the collision is assumed to remain constant throughout the deformation. Experiments are run with obliquities ranging from pure convergence (low obliquity) to pure strike slip (high obliquity). Reverse faults are observed for all obliquities with a nonzero convergent component. By contrast, only collisions with a large amount of strike slip motion exhibit wrench faulting. In experiments dominated by their convergent component, the strike slip motion is totally accommodated by oblique slip along the reverse faults. Strain partitioning between reverse faults and wrench faults is only observed for experiments run above a certain critical partitioning obliquity. Prom the observed initial faults, we can deduce the change in orientation in the principal stress triad as the obliquity is changed. We propose that the initial direction of maximum compressive stress (?1) rotates horizontally as the obliquity is changed, which in turn affects the geometry of the initial faults formed in the material. In the case of reverse faults, the rotation increases their dip measured along the direction of pure convergence. The relative magnitude of the minimum horizontal stress and the vertical stress determine whether reverse faults or strike slip faults are the first to form. Although long term deformation is more difficult to analyze, a simple relationship for the angle at which strain partitioning occurs is derived.
Burbidge, David R.; Braun, Jean
Relationship between outer forearc subsidence and plate boundary kinematics along the Northeast Japan convergent margin
NASA Astrophysics Data System (ADS)
Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives kilometer-scale outer forearc subsidence, has been purported to explain the evolution of nearly half the world's subduction margins, including part of the history of northeast Japan. Here, we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern Japan. A synthesis of newly updated analyses of outer forearc subsidence, the timing and kinematics of upper plate deformation, and the history of plate convergence along the Japan trench demonstrate that the onset of rapid fore-arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the Sea of Japan and with an acceleration in convergence rate at the trench. In Plio-Quaternary time, relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate. The coincidence of these changes across the forearc, arc, backarc system appears to require an explanation at the scale of the entire plate boundary. Similar observations along other western Pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule, rather than the exception. We suggest that a significant component of forearc subsidence at the northeast Japan margin is not the consequence of basal tectonic erosion, but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics. If correct, this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins.
Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Furlong, Kevin P.
Tectonic Plates and Plate Boundaries
NSDL National Science Digital Library
This interactive activity adapted from NASA features world maps that identify different sections of the Earth's crust called tectonic plates. The locations of different types of plate boundaries are also identified, including convergent, divergent, and transform boundaries.
Foundation, Wgbh E.
Subduction at Convergent Boundary
NSDL National Science Digital Library
The representation depicts subduction. The narrated animated movie (simulation) shows subduction of the Indian Plate as the Indian Plate and the Eurasian Plate converge at the plate boundary. The segment begins showing a world view of the Earth's plates and zooms in on the highlighted Indian and Eurasian plate activity. The animation transitions to a cross-sectional view, giving an inside-the-Earth look at what happens as these plates converge. The movie can be viewed in two ways- in continuous play or step by step.
Kinematic evolution of the Northeast Japan convergent margin and implications for plate boundary dynamics
NASA Astrophysics Data System (ADS)
Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives mass loss and subsidence of the outer forearc, has been invoked to explain the geologically recent evolution of nearly half the world's subduction margins. However, the mechanisms that initiate and sustain forearc subsidence are not well understood. We provide new analyses of the kinematic evolution of the northeast Japan margin, considered a type example of erosive margins, that demonstrate that vertical motions of the outer forearc are coincident with changes in upper plate kinematics and lower plate convergence rate. New constraints on the timing and kinematics of deformation along inner forearc faults indicate Plio-Quaternary inversion of Miocene extensional structures. The initiation of reverse slip along the inner forearc Futaba (5.6 to 3.9 Ma), Oritusme (5.9 to 4.8 Ma), and Noehij (Pliocene) faults are constrained by new U-Pb ages from tephras in growth strata. The initiation of an earlier phase of extension along the Oritusme and Futaba faults is identified from thick sequences of Miocene rift-related sediments in the hanging walls that are absent in the footwalls. Existing biostratigraphic and geochronolgic ages near the base of the syn-extensional sequences constrain the initiation of extension to 23.9-21.0 and ~20.8 Ma for the Futaba and Oritsume faults, and cross sections across these structures require nearly complete thrust inversion of Miocene extensional displacement. A regional synthesis of deformation demonstrates that the timing and kinematics of forearc deformation are contemporaneous with previously documented Miocene extension and Plio-Quaternary inversion in the backarc. Moreover, reconstructions of Pacific-Honshu convergence rates indicate that 1) the initiation of forearc subsidence and upper plate extension is coincident with a two to three fold increase in margin-perpendicular convergence, and 2) the onset of arc-normal shortening and increased frontal accretion occurred during a period of relatively constant convergence rate. The temporal correlation between deformation along upper plate faults, forearc subsidence, and lower plate convergence rates at the Northeast Japan margin suggests that the vertical motions of the forearc are likely governed by changes in lower plate kinematics. We hypothesize that an acceleration in plate convergence drives changes in slab geometry at shallow depths that allows for subsidence of the forearc, and suggest that a portion of the subsidence record previously interpreted as tectonic erosion instead reflects an upper plate response to plate boundary dynamics.
Regalla, C.; Fisher, D. M.; Furlong, K. P.; Kirby, E.
Localization Mechanisms of Melting and Melt Migration in the Mantle Wedge at Convergent Plate Boundaries
NASA Astrophysics Data System (ADS)
Along-strike magmatic segmentation with a 50-100 km scale has been recognized for several convergent plate boundaries, including the Aleutians, the Cascades (Marsh, 1979), and Japan (Tamura et al., 2002). Mantle wedge seismic velocity structure beneath Japan is also segmented with low seismic velocity columns beneath volcanic segments. Identifying plausible buoyant flow mechanisms that may lead to magmatic segmentation is thus an important aspect of understanding melting and melt migration in these settings. Reaction infiltration instability during melting has been identified as a possible mechanism of melt channelization (Aharonov et al. 1995; Spiegelman et al., 2001), but the predicted scale of several compaction lengths (1-200 m) appears to be too small for this mechanism alone to explain the observed segmentation. Thermal convection in the mantle wedge (Honda and Yoshida, 2005) may be driven by cool downwellings ~100 km in scale that develop at the base of the overriding plate. Decompression melting is thus localized in upwelling regions between the cool downwelling sheets aligned with plate motion. Convective flow in the mantle wedge of an appropriate scale might also be driven by instability of thickened crust beneath the magmatic arc (Behn et al., 2007), but a direct connection of this mechanism with melt production has not yet been explored. Instability may also result from buoyancy that develops along the top of the downgoing plate. Marsh and Carmichael (1974) proposed that melt generated along the top of the downgoing plate ascended diapirically; however recent evidence does not generally favor melting of the downgoing plate. Dehydration of the plate however releases hydrous fluid that should rise buoyant into the overlying mantle. Buoyant solid flow may hence develop due to the presence of hydrous fluid or low density serpentine (and other hydrous phases) formed in cool mantle just above the top of the downgoing plate. Serpentine formation involves a significant volume increase and serpentenized mantle is therefore less dense than dry mantle containing an equivalent amount of free water. Exothermic serpentine formation is limited by the heat of reaction. However, decreasing pressure in buoyantly ascending mantle allows the continuing formation of serpentine, thus leading to buoyant instability. Ongoing theoretical studies are exploring the conditions required for instability, the wavelength at which it would occur, and the physical properties of mantle materials that would make it possible.
Parmentier, E. M.; Cagnioncle, A.
Holocene turbidites reveal earthquake supercycles at a slow convergence plate boundary (Northern Algeria)
NASA Astrophysics Data System (ADS)
Ongoing evidence for earthquake clustering calls upon records over numerous earthquake cycles to improve seismic hazard assessments, especially at places where recurrence times overstep historical records. Here, we show that meaningful information of large earthquakes recurrence intervals over several seismic cycles may be obtained using turbidite record offshore the Algerian margin. The Africa-Eurasia plate boundary is slowly convergent (~3mm/yr), with deformation in the investigated margin segment accommodated mainly onland, along thrusts and strike-slip faults. Historically, two relatively large earthquakes stroke the area in 1954 (Orl�ansville M6.7) and 1980 (El Asnam M7.3). Holocene turbidites emplaced offshore are triggered by thirteen earthquakes. Most of them tune to paleoseismic record of the El Asnam fault onland, whereas two are slightly diachronous (<100 yrs), and likely result from bursts of activity on nearby faults. Turbidites depict a bimodal distribution over ~8 kyrs that support the concepts of earthquake supercycles and rupture synchronization between nearby faults. Thirteen coastal paleoquakes underpin clusters of 3 to 6 events with mean recurrence intervals of ~300-600 years, separated by two periods of quiescence of ~1.7 ka without major events on any fault. They imply alternation of broad phases of strain loading and shorter phases of strain release along the fault network. More generally, our results demonstrate that fault slip rates are time-dependent and that earthquake occurrence might be strain-predictable rather than time- or slip-predictable. Turbidite paleoseismology investigation is ongoing on an adjacent margin segment where the Boumerdes M6.9 earthquake occurred in 2003. Preliminary results retrieved the traces of historical earthquakes, and established Holocene time-series. They support a similar bimodal seismic distribution, suggesting that earthquake supercycling should be a major strain release process along the Africa-Eurasia plate boundary.
Ratzov, Gueorgui; Cattaneo, Antonio; Babonneau, Nathalie; Yelles, Karim; Bracene, Rabah; Lateb, Tassadite; D�verchere, Jacques
Recently active reverse faulting in the Atacama Basin area, northern Chile: Implications for the distribution of convergence across the western South America plate boundary
The western South American margin is one of the most active continental plate boundaries in the world. The ongoing convergence between the Nazca plate, or formerly the Farallon plate, and the South American plate produced the wide deformation belt of the Andes. In order to obtain more information about the active deformations in the central Andean belt to better understand
J. H. Shyu; G. Gonzalez; M. Simons; F. Aron; A. Veloso
Influence of cumulative convergence on lithospheric thrust fault development and topography along the Australian-Pacific plate boundary south of New Zealand
The development of faulting and topography resulting from initial convergence within oceanic lithosphere is largely unknown. We explore relationships among convergence, structural development, and topography along ?1500 km of the submarine Australian-Pacific plate boundary south of New Zealand, the Macquarie Ridge Complex (MRC). Due to the variable orientation of the boundary and close proximity of the Australian-Pacific poles of rotation,
T. A. Meckel; P. Mann; Sharon Mosher; Millard F. Coffin
Plate Tectonics II: Plates, plate boundaries, and driving forces
NSDL National Science Digital Library
The distribution of earthquakes and volcanoes around the world confirmed the theory of plate tectonics first proposed by Wegener. These phenomena also help categorize plate boundaries into three different types: convergent, divergent, and transform.
Egger, Anne
Tectonic Plates and Plate Boundaries (WMS)
NSDL National Science Digital Library
The earths crust is constantly in motion. Sections of the crust, called plates, push against each other due to forces from the molten interior of the earth. The areas where these plates collide often have increased volcanic and earthquake activity. These images show the locations of the plates and their boundaries in the earths crust. Convergent boundaries are areas where two plates are pushing against each other and one plate may be subducting under another. Divergent boundaries have two plates pulling away from each other and indicate regions where new land could be created. Transform boundaries are places where two plates are sliding against each other in opposite directions, and diffuse boundaries are places where two plates have the same relative motion. Numerous small microplates have been omitted from the plate image. These images have been derived from images made available by the United States Geological Surveys Earthquake Hazards Program.
Sokolowsky, Eric; Mitchell, Horace
Effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries
NASA Astrophysics Data System (ADS)
Hydrous fluids derived by dehydration of the downgoing slab at convergent plate boundaries are thought to provoke wet melting in the wedge above the downgoing plate. We have investigated the distribution of hydrous fluid and subsequent melt in the wedge using two-dimensional models that include solid mantle flow and associated temperature distributions along with buoyant fluid migration and melting. Solid mantle flow deflects hydrous fluid from their buoyant vertical migration through the wedge. Melting therefore does not occur directly above the region where hydrous fluids are released from the slab. A melting front develops where hydrous fluids first encounter mantle material hot enough to melt. Wet melting is influenced by solid flow through the advection of fertile mantle material into the wet melting region and the removal of depleted material. The region of maximum melting occurs where the maximum flux of water from slab mineral dehydration reaches the wet melting region. The extent of melting (F) and melt production rates increase with increasing convergence rate and grain size due to increased temperatures along the melting front and to increased fractions of water reaching the melting front, respectively. The position of isotherms above the wet solidus varies with increasing slab dip and thereby also influences F and melt production rates. Applying the understanding of wet melting from this study to geochemical studies of the Aleutians may help elucidate the processes influencing fluid migration and melt production in that region. Estimates of the timescale of fluid migration, seismic velocity variation, and attenuation are also investigated.
Cagnioncle, Amandine-Marie; Parmentier, E. M.; Elkins-Tanton, Linda T.
Deformation kinematics along oblique convergent plate boundary zones in the western United States, Japanese Islands, and Pakistan
NASA Astrophysics Data System (ADS)
Horizontal velocity gradient tensor field in the western U.S is estimated using moment tensors of earthquakes between 1850 to 1995. The velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5� of the NUVEL-1A Pacific-North American plate motion direction. The magnitude of the earthquake-related velocity is 62% of the NUVEL-1A total Pacific-North American plate motion. The total velocity obtained from the Quaternary fault slip rate data across the entire plate boundary is within 2 mm/yr of the NUVEL-1A predicted Pacific (PA)-North American (NA) plate motion velocity, but directions are 6� anticlockwise of directions given by NUVEL-1A. The total velocity obtained from inversion of recent geodetic data is 2�--3� anticlockwise from the NUVEL-1A NA-PA velocity, but the difference between the two is not significant at the 95% confidence level. Relative motions within the deforming Japanese Islands with respect to the Sea of Japan are determined using earthquake records over the last 414 years, slip rates on Quaternary faults, and angular change rates obtained from triangulation in the last century. The directions of the principal strain axes obtained from seismic, geological, and geodetic data are in general agreement with each other, with the maximum shortening axis oriented in a WNW direction. Intraplate deformation in southwestern Japan determined from the seismic data accommodates a velocity of 5.5 +/- 2 (1sigma) mm/yr in a direction parallel to the Nankai trough, which is about 25% of the plate motion velocity component parallel to the Nankai trough between the Philippine Sea and Eurasian plates. A comparison of shear strain rates, principal strain rates, and velocity fields determined from geodetic data with those calculated from the elastic dislocation models involving interplate motion at the Japan trench indicates that the geodetic strain field in northern Honshu is primarily elastic strain transmitted from the Japan trench. Horizontal strain rate and velocity field that accommodate India-Eurasia plate motion in Pakistan are determined based on constraints from geological and geodetic information in the region. The optimal model that yields a strain rate field consistent with observed geologic, seismologic, and geodetic data gives 17--28 mm/yr of left-lateral strike-slip motion along the Chaman fault zone, 3--6 mm/yr of east-west convergence and 5--14 mm/yr of north-south left-lateral shear across the roughly NS trending Sulaiman Range. (Abstract shortened by UMI.)
Shen-Tu, Bingming
Focal Mechanisms at the convergent plate boundary in Southern Aegean, Greece.
NASA Astrophysics Data System (ADS)
Greece is characterized by high seismicity, mainly due to the collision between the European and the African lithospheric plates and the dextral strike slip motion along the North Anatolia Fault zone and North Aegean Trough. The subduction of the Eastern Mediterranean oceanic plate along the Hellenic Arc under the Aegean microplate along with the accompanied roll back of the descending slab is considered the main tectonic feature of the region (Papazachos and Comninakis 1971; Makropoulos and Burton 1984; Papazachos et al. 2000a, b). The divergent motion between the Aegean block and mainland Europe is indicated by an extension zone in the northern Aegean, with Crete and Aegean diverging from mainland Europe at a rate of about 3.5 cm yr-1 with Africa moving northward relative to Europe at a rate of about 1 cm yr-1 (Dewey et al., 1989; Papazachos et al., 1998; Mc-Clusky et al., 2000; Reilinger et al., 2006). In this tectonically complicated area diverge types of deformation are manifested, in addition to the dominant subduction processes. Aiming to shed more light in the seismotectonic properties and faulting seismological data from the Hellenic Unified Seismological Network (HUSN) were selected and analyzed for determining focal mechanisms using the method of moment tensor inversion, additional to the ones being available from the routine moment tensor solutions and several publications. Thus, 31 new fault plane solutions for events with magnitude M>4.0, are presented in this study, by using the software of Ammon (Randall et al., 1995). For this scope the data from at least 4 stations were used with an adequate azimuthal coverage and with an epicentral distance not more than 350 km. The preparation of the data includes the deconvolution of instruments response, then the velocity was integrated to displacement and finally the horizontal components were rotated to radial and transverse. Following, the signal was inverted using the reflectivity method of Kennett (1983) as implemented by Randall (1994) in order to determine Green's functions. Initially, iterative inversions were performed considering a crude depth interval of 5 km and the relative misfit functions were computed. In a second stage, inversions were performed considering a finer depth interval of 1-2 km around the depth where the lowest misfit was exhibited. During the analysis different velocity models were used (Karagianni et al., 2005; Novotny et al., 2001; Papazachos et al., 1997). This research has been funded by the European Union (European Social Fund) and Greek national resources under the framework of the "THALES Program: SEISMO FEAR HELLARC" project of the "Education & Lifelong Learning" Operational Programme.
Moshou, Alexandra; Papadimitriou, Eleftheria; Drakatos, George; Evangelidis, Christos; Karakostas, Vasilios; Vallianatos, Filippos; Makropoulos, Konstantinos
ConcepTest: EQ and Convergent Boundary Sketch
NSDL National Science Digital Library
The figure below was drawn by a student to show the relationship between earthquake epicenters (filled circles) and a convergent plate boundary (red line). The figure represents a boundary between an oceanic plate ...
ConcepTest: Convergent Boundary
NSDL National Science Digital Library
A and B represent locations on two separate plates. The curved black line represents the plate boundary. The arrows show the directions of plate motion and the rates of motion are indicated. a. transform b. ...
Mapping Plate Tectonic Boundaries
NSDL National Science Digital Library
To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.
Kerwin, Michael
Revised tectonic boundaries in the Cocos Plate off Costa Rica: Implications for the segmentation of the convergent margin and for plate tectonic models
The oceanic Cocos Plate subducting beneath Costa Rica has a complex plate tectonic history resulting in segmentation. New lines of magnetic data clearly define tectonic boundaries which separate lithosphere formed at the East Pacific Rise from lithosphere formed at the Cocos-Nazca spreading center. They also define two early phase Cocos-Nazca spreading regimes and a major propagator. In addition to these
Udo Barckhausen; Cesar R. Ranero; R. von Huene; Steven C. Cande; Hans A. Roeser
Mountain Maker- Earth Shaker (Convergent Boundary: oceanic-continental)
NSDL National Science Digital Library
The representation depicts plate boundary interactions. The convergent boundary is one part of a larger interactive diagram (the 2nd slider/ arrow from the left), that focuses on an ocean plate pressing against a continental plate. This review specifically addresses the part of the resource dealing with what happens when plates pull apart. The "show intro" link provides instruction for diagram manipulation.
Recently active reverse faulting in the Atacama Basin area, northern Chile: Implications for the distribution of convergence across the western South America plate boundary
NASA Astrophysics Data System (ADS)
The western South American margin is one of the most active continental plate boundaries in the world. The ongoing convergence between the Nazca plate, or formerly the Farallon plate, and the South American plate produced the wide deformation belt of the Andes. In order to obtain more information about the active deformations in the central Andean belt to better understand the current distribution of convergence across the orogen, we attempted to map major structures that appear to be active recently by their topographic expressions using SRTM DEM and Landsat satellite images, followed by field observations. Results of our mapping show that there are many reverse faults that may be recently active in the area surrounding the Atacama Basin, in the Preandean Depression in northern Chile. These include a series of active reverse faults and related folds at the southeastern corner of the Atacama Basin, a major fold system that may be produced by an underlying fault just east of the basin, and a series of folds that forms the Cordillera de la Sal in the northern and western part of the basin. At the southeastern corner of the Atacama Basin, several geomorphic features indicate that at least some of the structures there have been active quite recently, including small drainages that cut through the folds and form active alluvial fans. Similar features of active river incision across folds are also present in the northern part of the basin. The fold system east of the basin may be one of the most important structures in the area. Deformed lava flows and deflected drainages indicate that this structure has been active recently, and growth strata near the fold suggest that it has been active for several myr. If so, the structure may be a major reverse fault system that defines the eastern boundary of the Atacama Basin, and may thus be an important onland structure that is responsible for absorbing part of the plate convergence.
Shyu, J. H.; Gonzalez, G.; Simons, M.; Aron, F.; Veloso, A.
Investigating the strain accumulation of upper plate faults at the N-Chilean convergent plate boundary at different spatial and temporal scales
NASA Astrophysics Data System (ADS)
According to recent paleoseismological investigations (Cort�s et al., 2012), upper plate faults located at the N-Chilean convergent plate boundary well above the coupling zone of the subduction interface are capable of generating large earthquakes of up to Mw=7. We have chosen four active upper plate faults characterized by surface ruptures to investigate their activity and the processes responsible for strain accumulation. In this study, we use a combination of creepmeter time series and high-resolution topography data to assess fault deformation on spatial scales ranging from microns to meters and on temporal scales ranging from seconds to the geomorphological timescale (102-104 yrs). To investigate the short-term deformation signals, we monitor the target faults with an array of creepmeters at a sampling rate of 30 seconds and a resolution of 1 ?m. Despite the fact that long-term displacement rates range between 0.2-0.3 mm/yr for the 103-105 year timescale, displacement rates measured since 2008 are of the order of only a few ?m/yr to approx. 80 ?m/yr. There is no pronounced steady-state creep on the monitored faults. Time series analysis shows a few creep events, and numerous Sudden Displacement Events (SDEs) ranging from 1-59 ?m. The sum of SDEs accounts for a significant part of the cumulative displacement (e.g. Salar del Carmen Fault: 50-60 %, Cerro Fortuna Fault: >90 %), but is an order of magnitude less than the long-term displacement rates. To assess the long-term behavior of the monitored fault segments, high-resolution topography data has been acquired with Differential-GPS by measuring profiles perpendicular to the fault scarps and along incised gullies. The data show clear differences between individual segments of the target faults concerning the total fault scarp height, which is used as a proxy for cumulative displacement. The profiles enable us to distinguish single, composite and multiple scarps; allowing us to capture the number of seismic events that contributed to the creation of the fault scarp. Profiles measured inside gullies allow us to detect knickpoints used as proxy for seismic faulting and thus to quantify the number of events as well as the individual displacement per event. Fault scarp heights and styles/shapes as well as the amount and the height of knickpoints vary predominantly near step-overs, bends and between fault segments. This suggests individual deformation histories of the studied fault segments, possibly depending on their orientations and the local stress conditions both influencing the time dependent strain accumulation pattern. Displacements measured at knickpoints account for approx. 5-40 % of the cumulative displacement. This leaves a significant fraction of displacement probably accumulated by alternative processes, e.g. creep. Comparing the instrumental record with the long-term deformation of the studied fault segments, we note that, according to the instrumental observation, no pronounced steady-state creep could be observed in the recent past of the target faults. In contrast, the topographic data suggest that a significant part of strain was accumulated by aseismic processes. We propose that strain accumulation of the studied faults is highly variable in time, possibly driven or influenced by the stage of the megathrust seismic cycle.
Ewiak, O.; Victor, P.; Ziegenhagen, T.; Oncken, O.
Tectonic Plates and Plate Boundaries
NSDL National Science Digital Library
Continents were once thought to be static, locked tight in their positions in Earth's crust. Similarities between distant coastlines, such as those on opposite sides of the Atlantic, were thought to be the work of a scientist's overactive imagination, or, if real, the result of erosion on a massive scale. This interactive feature shows 11 tectonic plates and their names, the continents that occupy them, and the types of boundaries between them.
Large tectonic rotations since the Early Miocene in a convergent plate-boundary zone, South Island, New Zealand
NASA Astrophysics Data System (ADS)
A palaeomagnetic study in part of the New Zealand plate-boundary zone provides new constraints on the temporal and spatial distribution of Neogene and Quaternary tectonic rotations. Thermal demagnetization of samples from Cretaceous basaltic dykes, Palaeocene-Oligocene micritic limestone, and Miocene and Pliocene siltstones in the Marlborough region, South Island, have defined stable, high-temperature magnetic components, which are interpreted as the primary magnetization. Declination anomalies, after tectonic corrections, are interpreted as rigid body rotations about a vertical axis of sample sites relative to the Pacific plate. All palaeomagnetic data from Marlborough cluster into three main groups. A 60-100� clockwise rotation affected Palaeocene to Middle Miocene sedimentary sequences across Marlborough between � 18 Ma and � 8 Ma, coeval with a phase of low-angle thrusting. The absence of this rotation in a Late Cretaceous dyke swarm defines the present western limit of the early rotating zone. A regional � 20� clockwise rotation occurred in the last 4 Ma during the development of the Marlborough Fault System in a zone of dextral transpression, although locally clockwise rotations ? 40� may have occurred near some of the major dextral strike-slip faults. However, a negligible rotation is observed in the same period in the region to the southeast of the major Kekerengu dextral strike-slip fault, which appears to have acted as a hinge zone, accommodating relative rotation by dextral strike-slip on an arcuate fault, bending, and internal deformation. The observed tectonic rotations record the overall clockwise rotation of the trend of the southern end of the Hikurangi margin from W to NW in the Early Miocene to � NE today, determined independently from the long-term relative plate motion data for the Pacific and Australian plates.
Vickery, Sara; Lamb, Simon
ConcepTest: Convergent Boundary
NSDL National Science Digital Library
The figures below show the location of a plate boundary (dashed line) and the distribution of earthquake foci (filled circles). The color of the filled circle indicates the depth of the earthquake focus. Given the ...
NSDL National Science Digital Library
Discovering Plate Boundaries is based on 5 world maps containing earthquake, volcano, topography, satellite gravity, and seafloor age data. The novel aspect of the exercise is the "jigsaw" manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it useful at a wide variety of levels; it has been used successfully in 5th grade classes, as well as in non-major earth science classes. The exercise is based on a set of wall maps that are not consumed during the exercise. Other inexpensive materials required include two 11x17 black and white copies per student and colored pencils. Because the exercise is not based on student access to the web, it is not dependent on classroom technology equipment. The exercise takes three 50-minute class periods to complete, and involves the students in making presentations to one another in small groups as well as to the whole class. The students come away from the exercise with knowledge of the key features of each type of plate boundary and a sense of why each looks and acts the way it does.
Sawyer, Dale
Effective strength of incoming sediments and its implications for plate boundary propagation: Nankai and Costa Rica as type examples of accreting vs. erosive convergent margins
NASA Astrophysics Data System (ADS)
The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile.
Kopf, Achim
Isotopic composition of helium, and CO[sub 2] and CH[sub 4] contents in gases produced along the New Zealand part of a convergent plate boundary
New Zealand straddles an active tectonic boundary between the Indo-Australian and Pacific plates. To the NE and SW oblique convergence of oceanic and continental crusts leads to the establishment of subduction zones; in the center continental crusts collide along a transform boundary. With regard to mantle degassing, and on the basis of chemical and He isotopic analyses of 140 samples from all over New Zealand, four major environments can be distinguished: (1) R/R[sub A] values approaching MORB values are observed in areas of andesitic and rhyolitic volcanisms and high-temperature geothermal activity over the center of the North Island. C/[sup 3]He ratios there vary from <10 [times] 10[sup 9], typical of volatiles released from the mantle, in the W, to >40 [times] 10[sup 9], suggesting considerable addition of CO[sub 2] from other than mantle sources, in the E. (2) In areas of recent igneous activity, residual mantle He is extracted from rocks through hydrothermal alteration by percolating groundwater. The gases are low in CO[sub 2] due to conversion to carbonate; any CH[sub 4] present is generated within the crust. C/[sup 3]He ratios are generally well below those of any magmatic vapor. (3) In the absence of recent igneous activity, but in areas of increased seismicity, mantle He may reach the surface along fractures provided by the movement of the subducting slab in forearc regions or by dilatancy pumping or fault-valving in highly compressional, but seismically active parts of an orogenic plate boundary. (4) Mantle degassing is greatly impeded in areas of crustal thickening as indicated by negative gravity anomalies, low seismicity and rapid uplift. There [sup 3]He/[sup 4]He ratios approach typical crustal values of <0.1 R[sub A]. Except in areas of present-day volcanic and geothermal activity, production, transport, storage, and release processes of [sup 3]He, CO[sub 2], and CH[sub 4] appear to be effectively decoupled.
Giggenbach, W.F. (Institute of Geological and Nuclear Sciences, Lower Hutt (New Zealand)); Sano, Y. (Hiroshima Univ. (Japan)); Wakita, H. (Univ. of Tokyo (Japan))
The Role of Serpentinites at Convergent Plate Boundaries: Using New Discoveries to Facilitate the Learning of Major Earth Processes
NASA Astrophysics Data System (ADS)
A benefit of integrating a vital educational enterprise into a cutting-edge funded research initiative is the ability to bring new scientific discoveries quickly into the classroom without being bound to the textbook publication cycle. A key objective the MARGINS Data in the Classroom project was to facilitate the discovery-to-the-classroom transition of knowledge through the development of Web-deliverable, modular MARGINS �Mini-Lessons�. Some 34 Mini-Lessons are available for classroom use at http://serc.carleton.edu/margins/collection.html, and the development of new Mini-Lessons is a listed Education/Outreach priority of the successor GeoPRISMS Program. An important discovery that arose from the MARGINS Subduction Factory Initiative was the recognition that serpentinites - metamorphically hydrated products of ultramafic rocks rich in serpentine group minerals - are significant constituents of both the mantle wedge and downgoing plate. Serpentines are interesting mineralogically because of their distinctive physical properties, habits and appearance; and for their close affinities with olivine and Mg-rich pyroxenes. Given that serpentines primarily form through the hydration of olivine or Mg-rich pyroxenes, serpentinites constitute a reservoir of subduction-related H2O and entrained trace species in modified mantle rocks of the wedge or slab. As well, serpentine group minerals are interesting rheologically because, as sheet silicates, they can behave in a plastic fashion in rocks that are undergoing deformation, and can thus flow along faults in response to deforming stresses, or be easily entrained in fault rock assemblages along a subduction thrust. Two different MARGINS Mini-Lessons address the issue of serpentinite in subduction zone settings, focusing primarily on the observed occurrences of serpentinite seamounts in the forearc regions of the Mariana subduction system, a MARGINS Subduction Factory Focus Site, and their geochemical and geodynamic implications (e.g., Savov et al 2007); and also on the geophysical inferences of DeShon and Schwartz (2004) and Syracuse et al (2006) as to the presence of abundant serpentinite in different parts of the MARGINS Central American subduction system Focus Site. The Mini-Lesson seeks to lead students through the arguments made in these very recent papers, both through an analysis of the presented data, and through GeoMapApp examinations of bathymetric and geochemical datasets that students can access independently. The instructional approach is one of guided inquiry, with learning goals focused on a deeper understanding of the subduction process through examining its geochemical and geodynamic implications, as well as providing students with experience in the critical reading of the scientific literature and the extraction of useful information from technical papers.
Ryan, J. G.
Seismic gaps and plate tectonics: Seismic potential for major boundaries
The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by
W. R. McCann; S. P. Nishenko; L. R. Sykes; J. Krause
A new class of transform plate boundary
NASA Astrophysics Data System (ADS)
The theory of plate tectonics postulates that the relative motion between two neighboring plates occurs along three types of boundaries: divergent (spreading center, rift), convergent (subduction, collision), and horizontal (transform). Because the theory assumes rigid behavior of plates, transform plate boundaries must lie along small circles around the pole of rotation of relative motion between two neighboring plates. However, global models of current plate motion (e.g., NUVEL-1A) show that several boundaries with significant horizontal motion (i.e., the Dead Sea Fault and the Eastern Andean Frontal Fault Zone) do not lie along small circles but rather intersect the circles at 45�. The orientation of these faults can be explained by a new theory of intraplate tectonics, which predicts the first-order intraplate stress field in terms of small circles, great circles, and spiral lines that intersect both sets of circles at 45�. According to the theory, these transform faults are situated along the 45� spiral lines and follow the direction of maximum horizontal shear stress. The theory also predicts that the direction of interseismic relative plate motion between the two plates should be oriented at 45� to the transform plate boundary; this prediction can be tested within a few years using space geodesy. The alignment of these faults along spiral lines is explained by the theory's predicted stress field and a plasticity (von Mises) yield stress criterion for earthquake rupture. It is suggested that these faults represent a new class of transform plate boundary between large deformable plates and not between rigid sub-plates, as formerly postulated.
Wdowinski, S.
Metamorphism in Plate Boundary Zones
NASA Astrophysics Data System (ADS)
Accretionary orogenic systems (AOS) form at sites of subduction of oceanic lithosphere; these systems dominate during supercontinent break-up and dispersal. Collisional orogenic systems (COS) form where ocean basins close and subduction ultimately ceases; these systems dominate during crustal aggregation and assembly of supercontinents. It follows that COS may be superimposed on AOS, although AOS may exist for 100s Ma without terminal collision. AOS are of two types, extensional-contractional AOS in dominantly extensional arc systems, and terrane-dominated AOS in which accretion of allochthonous elements occurs during oblique convergence. On modern Earth, regional metamorphism occurs in plate boundary zones. Blueschists are created in the subduction zone and ultra-high pressure metamorphic (UHPM) rocks are created in collision zones due to deep subduction of continental lithosphere; granulites are created deep under continental and oceanic plateaus and in arcs and collision zones [high-pressure (HP) granulites, ultra-high temperature (UHT) granulites]. In extensional-contractional AOS, basement generally is not exposed, primitive volcanic rocks occur through the history, rift basins step oceanward with time, and a well-defined arc generally is absent. LP-HT metamorphism is dominant, with looping, CW or CCW P-T-t paths and peak metamorphic mineral growth syn-to-late in relation to tectonic fabrics. UHT and HP granulites are absent, and although rare, blueschists may occur early, but UHPM is not recorded. Short-lived contractional phases of orogenesis probably relate to interruptions in the continuity of subduction caused by features on the ocean plate, particularly plateaus. Extensive granite (s.l.) magmatism accompanies metamorphism. Examples include the Lachlan Orogen, Australia, the Acadian Orogen, NE USA and Maritime Canada, and the Proterozoic orogens of the SW USA. At plate boundaries, oblique convergence is partitioned into two components, one directed more orthogonal to the strike of the trench than the convergence vector, and the other directed parallel to the strike of the trench. The orthogonal component is accommodated by subduction, but the margin-parallel component gives rise to block rotations and extension, strike-slip motion, and shortening within the upper plate. In some AOS, it has been argued that `paired' metamorphic belts characterize the metamorphic pattern. Commonly, this is a false construct that results from failure to recognize orogen-parallel terrane migration and the limitations of particular chronological datasets. Whereas a HP-LT (blueschist-eclogite) metamorphic belt may occur outboard, it is generally separated from a LP-HT (And-Sil type) metamorphic belt by a terrane boundary. These are terrane-dominated AOS. In some AOS an additional feature of the orogenic process is ridge subduction, which is reflected in the pattern of LP-HT metamorphism and the magmatism. Granulites may occur at the highest grade of metamorphism in the LP-HT belt, where granite (s.l.) magmatism is common, but UHPM occurs only rarely in the outboard HP-LT belt. Examples include the Mesozoic metamorphic belts of Japan and the North American Cordillera. COS commonly are characterized by syntectonic index minerals that record CW P-T-t paths and Barrovian-type metamorphic field gradients generated by thickening followed by exhumation. However, during the Neoproterozoic, ultra-high temperature granulite facies metamorphism is common in orogens that suture Gondwana, whereas during the Phanerozoic, metamorphism to high-pressure granulite/medium temperature eclogite facies and extreme UHPM conditions commonly occurs and may be more typical of younger COS; examples include the Alpides, the Qinling - Dabie Shan - Sulu orogens, the Variscides and the Caledonides.
Brown, M.
Investigating the deformation of upper crustal faults at the N-Chilean convergent plate boundary at different scales using high-resolution topography datasets and creepmeter measurements
NASA Astrophysics Data System (ADS)
The Chilean convergent plate boundary is one of the tectonically most active regions on earth and prone to large megathrust earthquakes as e. g. the 2010 Mw 8.8 Maule earthquake which ruptured a mature seismic gap in south-central Chile. In northern Chile historical data suggests the existence of a seismic gap between Arica and Mejillones Peninsula (MP), which has not ruptured since 1877. Further south, the 1995 Mw 8.0 Antofagasta earthquake ruptured the subduction interface between MP and Taltal. In this study we investigate the deformation at four active upper plate faults (dip-slip and strike-slip) located above the coupling zone of the subduction interface. The target faults (Mejillones Fault - MF, Salar del Carmen Fault - SCF, Cerro Fortuna Fault - CFF, Chomache Fault - CF) are situated in forearc segments, which are in different stages of the megathrust seismic cycle. The main question of this study is how strain is accumulated in the overriding plate, what is the response of the target faults to the megathrust seismic cycle and what are the mechanisms / processes involved. The hyper arid conditions of the Atacama desert and the extremely low erosion rates enable us to investigate geomorphic markers, e .g. fault scarps and knickpoints, which serve as a record for upper crustal deformation and fault activity about ten thousands years into the past. Fault scarp data has been acquired with Differential-GPS by measuring high-resolution topographic profiles perpendicular to the fault scarps and along incised gullies. The topographic data show clear variations between the target faults which possibly result from their position within the forearc. The surveyed faults, e. g. the SCF, exhibit clear along strike variations in the morphology of surface ruptures attributed to seismic events and can be subdivided into individual segments. The data allows us to distinguish single, composite and multiple fault scarps and thus to detect differences in fault growth initiated either by seismic rupture or fault creep. Additional information on the number of seismic events responsible for the cumulative displacement can be derived from the mapping of knickpoints. By reconstructing the stress field responsible for the formation of identified seismic surface ruptures we can determine stress conditions for failure of upper crustal faults. Comparing these paleo stress conditions with the recent forearc stresses (interseismic / coseismic) we can derive information about a possible activation of upper crustal faults during the megathrust seismic cycle. In addition to the morphotectonic surveys we explore the recent deformation of the target faults by analyzing time series of displacements recorded with micron precision by an array of creepmeters at the target faults for over three years. Total displacement is composed of steady state creep, creep events and sudden displacement events (SDEs) related to seismic rupture. The percentage of SDEs accounts for >50 % (SCF) to 90 % (CFF) of the cumulative displacement. This result very well reflects the field observation that a considerable amount of the total displacement has been accumulated during multiple seismic events.
Ewiak, O.; Victor, P.; Ziegenhagen, T.; Oncken, O.
The dynamics of convergent boundaries over a convecting mantle
NASA Astrophysics Data System (ADS)
Attempts to explore the dynamics of convergent boundaries are essentially based on the confrontation of the observed kinematics to the intrinsic dynamic properties of subduction zones. Which often mismatch. On the basis of the mantle flow model of Conrad and Behn (2010), I explore the role of the often neglected basal drag that the flowing mantle exerts underneath each plate. After computing the total torque underneath each plate, I find that (i) the net torque due to basal drag systematically drives plates away from their ridges and towards subduction zones, conformably to the plate circuit; (ii) compressive zones are found where the net drag forces from upper and lower plates are converging, and diverging for extensive zones; (iii) trench migration is dictated by the difference between the upper plate drag force and lower plate drag force. In other words, trenches advance where upper plates pulls the subduction zones and the lower plate pushes it. These results indicate that differences in the dynamics of plate boundaries arise from the global mantle circulation more than the from the local properties of subduction zones. The often neglected drag force thus appears crucial to reconcile the kinematics and dynamics of subduction zones.
Husson, L.
The tectonic expression slab pull at continental convergent boundaries
NASA Astrophysics Data System (ADS)
Examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style, topographic elevation, denudation, metamorphism, postcollisional convergence, and foredeep basin geometry and facies. The distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary. At subduction boundaries where the rate of overall plate convergence is less than the rate of subduction (termed here retreating subduction boundaries) the transmission of horizontal compressive stress across the plate boundary is small, and regional deformation of the overriding plate is by horizontal extension. The tectonic expression of these retreating subduction boundaries includes topographically low mountains, little erosion or denudation, low-grade to no metamorphism, little to no involvement of crystalline basement in shortening, little to no postcollisional convergence, anomalously deep foredeep basins, and a protracted history of flysch deposition within the adjacent foredeep basin. Analysis of deflection and gravity data across three retreating subduction boundaries (Apennine, Carpathian and Hellenic systems) shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km (Carpathians), 50 and 150 km (Apennines) and 50 and 250 km (Hellenides). The total mass anomalies represented by the slabs are approximately 3�1012, 6�1012 and 12�1012 N/m, respectively. The slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland, and partially supported by dynamic (viscous) stresses in the asthenosphere. At subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction (termed here advancing subduction boundaries) the transmission of horizontal compressive stress across the plate boundary is large, and regional deformation of the overriding plate is by horizontal shortening. The tectonic expression of these advancing subduction boundaries includes topographically high mountains, antithetic thrust belts, large amounts of erosion and denudation, exposure of high-grade metamorphic rocks at the surface, extensive deformation of crystalline basement to midcrustal depths, protracted postcollisional convergence (tens of millions of years), and a protracted history of molasse deposition within the adjacent foredeep basins. Analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere (Western to Eastern and Southern Alps and Himalayas) shows that the thrust sheets have been translated for great distances over the foreland lithosphere (relative to the point at which the subduction forces are applied), thus obscuring any flexural and gravity signals from the subducted slab. However, it appears that far-field stresses, presumably related to global plate motions, drive most of the convergent motion across these subduction boundaries. The concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved. Appendix B is available with entire article on microfiche.Order from the American Geophysical Union, 2000 FloridaAvenue, N.W., Washington, D.C. 20009. Document T92-004; $2.50. Payment must accompany order.
Royden, Leigh H.
Observe animations of processes that occur along plate boundaries
NSDL National Science Digital Library
Here are three animations that reveal how tectonic plates move relative to each other at three types of plate boundaries--transform, convergent, and divergent boundaries. Key features such as the asthenosphere are labeled in the animations. In addition, each animation is equipped with movie control buttons that allow students to play, pause, and move forward and backward through each clip. The animation of a transform boundary shows the North American and Pacific plates sliding past one another, while an oceanic plate subducts under a continental plate producing volcanic activity in the convergent boundary animation. Two coordinated movie clips are used to demonstrate what occurs at a divergent boundary from different viewpoints. Copyright 2005 Eisenhower National Clearinghouse
Education, Terc. C.; Littell, Mcdougal
The seismotectonics of plate boundaries
NASA Technical Reports Server (NTRS)
Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.
Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.
HMK 1_Plate Boundaries: Present, future, & past
NSDL National Science Digital Library
Prior to this homework assignment, students will have been exposed (for ~2-3 in class activities and lectures) to general concepts in plate tectonics, plate boundaries, hot spot volcanoes, use of earthquake/volcano trends at plate boundaries, as well as GPS as a modern use to document plate motion. Students receive this activity as a homework assignment to be completed outside of class. Their task is to use provided topographic/bathymetric data, earthquake and volcano distribution, GPS data, as well as ocean floor and hot spot age trends to characterize plate motion in modern, future, and ancient plate boundaries. This is a three-part exercise that involves a modern plate boundary study form the eastern margin of the Pacific plate, a potential future plate boundary in eastern Africa, and a identification of possible ancient plate boundaries in the Eurasian plate.
Hampton, Brian
Flat plate puncture test convergence study.
The ASME Task Group on Computational Mechanics for Explicit Dynamics is investigating the types of finite element models needed to accurately solve various problems that occur frequently in cask design. One type of problem is the 1-meter impact onto a puncture spike. The work described in this paper considers this impact for a relatively thin-walled shell, represented as a flat plate. The effects of mesh refinement, friction coefficient, material models, and finite element code will be discussed. The actual punch, as defined in the transport regulations, is 15 cm in diameter with a corner radius of no more than 6 mm. The punch used in the initial part of this study has the same diameter, but has a corner radius of 25 mm. This more rounded punch was used to allow convergence of the solution with a coarser mesh. A future task will be to investigate the effect of having a punch with a smaller corner radius. The 25-cm thick type 304 stainless steel plate that represents the cask wall is 1 meter in diameter and has added mass on the edge to represent the remainder of the cask. The amount of added mass to use was calculated using Nelm's equation, an empirically derived relationship between weight, wall thickness, and ultimate strength that prevents punch through. The outer edge of the plate is restrained so that it can only move in the direction parallel to the axis of the punch. Results that are compared include the deflection at the edge of the plate, the deflection at the center of the plate, the plastic strains at radius r=50 cm and r=100 cm , and qualitatively, the distribution of plastic strains. The strains of interest are those on the surface of the plate, not the integration point strains. Because cask designers are using analyses of this type to determine if shell will puncture, a failure theory, including the effect of the tri-axial nature of the stress state, is also discussed. The results of this study will help to determine what constitutes an adequate finite element model for analyzing the puncture hypothetical accident.
Snow, Spencer (Idaho National Laboratories); Ammerman, Douglas James; Molitoris, David (Westinghouse); Tso, Chi-Fung (ARUP); Yaksh, Mike (NAC International)
Three-dimensional mechanics of Yakutat convergence in the southern Alaskan plate corner
NASA Astrophysics Data System (ADS)
Three-dimensional numerical models are used to investigate the mechanical evolution of the southern Alaskan plate corner where the Yakutat and the Pacific plates converge on the North American plate. The evolving model plate boundary consists of Convergent, Lateral, and Subduction subboundaries with flow separation of incoming material into upward or downward trajectories forming dual, nonlinear advective thermal/mechanical anomalies that fix the position of major subaerial mountain belts. The model convergent subboundary evolves into two teleconnected orogens: Inlet and Outlet orogens form at locations that correspond with the St. Elias and the Central Alaska Range, respectively, linked to the East by the Lateral boundary. Basins form parallel to the orogens in response to the downward component of velocity associated with subduction. Strain along the Lateral subboundary varies as a function of orogen rheology and magnitude and distribution of erosion. Strain-dependent shear resistance of the plate boundary associated with the shallow subduction zone controls the position of the Inlet orogen. The linkages among these plate boundaries display maximum shear strain rates in the horizontal and vertical planes where the Lateral subboundary joins the Inlet and Outlet orogens. The location of the strain maxima shifts with time as the separation of the Inlet and Outlet orogens increases. The spatiotemporal predictions of the model are consistent with observed exhumation histories deduced from thermochronology, as well as stratigraphic studies of synorogenic deposits. In addition, the complex structural evolution of the St Elias region is broadly consistent with the predicted strain field evolution.
Koons, P. O.; Hooks, B. P.; Pavlis, T.; Upton, P.; Barker, A. D.
Tectonics of the Jurassic-Early Cretaceous magmatic arc of the north Chilean Coastal Cordillera (22�-26�S): A story of crustal deformation along a convergent plate boundary
The tectonic evolution of a continental magmatic arc that was active in the north Chilean Coastal Cordillera in Jurassic-Early Cretaceous times is described in order to show the relationship between arc deformation and plate convergence. During stage I (circa 195-155 Ma) a variety of structures formed at deep to shallow crustal levels, indicating sinistral arc-parallel strike-slip movements. From deep crustal
Ekkehard Scheuber; Gabriel Gonzalez
Coupling of strain rate, orogen width and plate convergence speed in continental collisions
NASA Astrophysics Data System (ADS)
Most models that describe the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary. Yet a growing body of evidence in the Tibetan orogen suggests that deformation occurred early in the orogen's history at the far northern extent of the modern plateau and thus, our current mechanical understanding of orogenic plateau development is incomplete. Regardless of whether or not high topography was built simultaneously as a result of this deformation, early Cenozoic - present deformation in northern Tibet signifies that the modern limit of the orogen has been held fixed since continental collision began. Therefore strain has not significantly propagated further away from the plate boundary in time and the orogen width has narrowed as convergence continued since collision. Using a uniform average strain rate across the plateau derived from geodetic measurements, I predict changes in plate convergence rate through time as the orogen narrows. Observed decreases in plate convergence speed of India with respect to Eurasia through the Cenozoic (Molnar and Stock, in press) can be explained by the simple condition of a fixed orogen boundary and constant strain rate. This same relationship can also be derived for the Arabian-Eurasia collision however fewer geologic data and fewer plate velocity measurements are available to constrain such a model compared to Tibet.
Clark, M. K.
Turbulences in Boundary Layer of Flat Plates
NASA Astrophysics Data System (ADS)
The aeroelastic assessment of turbulences appearing in boundary layer of flat plates tested in the wind tunnel is treated in present paper. The approach suggested takes into account multiple functions in the analysis of flat plates subjected to laminar and turbulent wind forcing. Analysis and experimental assessments in the aerodynamic tunnel are presented. Some results obtained are discussed
Tesar, Alexander
Tectonics of the Jurassic-Early Cretaceous magmatic arc of the north Chilean Coastal Cordillera (22�-26�S): A story of crustal deformation along a convergent plate boundary
NASA Astrophysics Data System (ADS)
The tectonic evolution of a continental magmatic arc that was active in the north Chilean Coastal Cordillera in Jurassic-Early Cretaceous times is described in order to show the relationship between arc deformation and plate convergence. During stage I (circa 195-155 Ma) a variety of structures formed at deep to shallow crustal levels, indicating sinistral arc-parallel strike-slip movements. From deep crustal levels a sequence of structures is described, starting with the formation of a broad belt of plutonic rocks which were sheared under granulite to amphibolite facies conditions (Bolfin Complex). The high-grade deformation was followed by the formation of two sets of conjugate greenschist facies shear zones showing strike-slip and thrust kinematics with a NW-SE directed maximum horizontal shortening, i.e., parallel to the probable Late Jurassic vector of plate convergence. A kinematic pattern compatible to this plate convergence is displayed by nonmetamorphic folds, thrusts, and high-angle normal faults which formed during the same time interval as the discrete shear zones. During stage II (160-150 Ma), strong arc-normal extension is revealed by brittle low-angle normal faults at shallow levels and some ductile normal faults and the intrusion of extended plutons at deeper levels. During stage III (155-147 Ma), two reversals in the stress regime took place indicated by two generations of dikes, an older one trending NE-SW and a younger one trending NW-SE. Sinistral strike-slip movements also prevailed during stage IV (until �125 Ma) when the Atacama Fault Zone originated as a sinistral trench-linked strike-slip fault. The tectonic evolution of the magmatic arc is interpreted in terms of coupling and decoupling between the downgoing and overriding plates. The structures of stages I and IV suggest that stress transmission due to seismic coupling between the plates was probably responsible for these deformations. However, decoupling of the plates occurred possibly due to a decrease in convergence rate resulting in extension and the reversals of stages II and III.
Scheuber, Ekkehard; Gonzalez, Gabriel
Statistical tests of additional plate boundaries from plate motion inversions
NASA Technical Reports Server (NTRS)
The application of the F-ratio test, a standard statistical technique, to the results of relative plate motion inversions has been investigated. The method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance. This approach appears to be useful in determining whether additional plate boundaries are justified. Previous results have been confirmed favoring separate North American and South American plates with a boundary located beween 30 N and the equator. Using Chase's global relative motion data, it is shown that in addition to separate West African and Somalian plates, separate West Indian and Australian plates, with a best-fitting boundary between 70 E and 90 E, can be resolved. These results are generally consistent with the observation that the Indian plate's internal deformation extends somewhat westward of the Ninetyeast Ridge. The relative motion pole is similar to Minster and Jordan's and predicts the NW-SE compression observed in earthquake mechanisms near the Ninetyeast Ridge.
Stein, S.; Gordon, R. G.
Absolute plate motions by boundary velocity minimizations
NASA Technical Reports Server (NTRS)
The main interaction of the earth's interior with the lithosphere is as a material source and sink. An absolute reference frame defined by minimizing the translational motion of tectonic plate boundaries differs by 0.6 cm/year from a frame defined by hot spot traces and by 0.4 cm/year from the frame defined by the most plausible model of drag forces on the plates. The rms absolute translational velocities are about 2 cm/year for ocean-ocean plate boundaries and 1.5 cm/year for ocean-continent plate boundaries. The close agreement between the source and sink and the drag-dependent definitions suggests that the lithosphere, as a stress guide, to some extent controls the locations of its sources and sinks.
Kaula, W. M.
BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary
NASA Astrophysics Data System (ADS)
The southern Caribbean-South American plate boundary has many similarities to California's San Andreas system: 1) The CAR-SA system consists of a series of strands of active right lateral strike-slip faults extending >1000 km from the Antilles subduction zone. This system has several names and includes the El Pilar, Coche, San Sebastian, Moron, and Oca faults. 2) The CAR-SA relative velocity has been about 20 mm/yr of mostly right lateral motion since about 55 Ma, giving a total displacement on the CAR-SA plate boundary similar to that of the San Andreas system. 3) The plate boundary has about 10% convergence in western SA, with less as one moves eastward due to relative convergence between North and South America. 4) The CAR-SA system has fold and thrust belts best developed continentward of the strike-slip faults, similar to the San Andreas. 5) There is a big bend in the CAR plate boundary at approximately the same distance from the Antilles trench as the big bend in Southern California is from the Cascadia subduction zone. The tectonic origins of the CAR-SA plate boundary and the San Andreas are very different, however, despite the similarities between the systems. Rather than impingement of a ridge on a trench, the CAR-SA system is thought to have resulted from a continuous oblique collision of the southern end of a Cretaceous island arc system with the northern edge of South America. During this process the CAR island arc and the modern CAR plate overrode a proto-Caribbean plate and destroyed a Mesozoic passive margin on the northern edge of SA. BOLIVAR and GEODINOS are multi-disciplinary investigations of the lithosphere and deeper structures associated with the diffuse CAR-SA plate boundary zone. We review a number of observations regarding the plate boundary obtained or confirmed from these studies: 1) The Caribbean Large Igneous Province, being overridden by the Maracaibo block in western Venezuela, can be identified beneath Aruba and coastal Venezuela, and is associated with broad uplift of the coastal regions. This is likely a site of continental growth. 2) The accretionary wedge terranes of the Southern Caribbean Deformed Belt formed in the Neogene, and extend as far east as the Aves Ridge. They result from SA overriding the CAR LIP, which for a number of reasons, we do not regard as normal subduction. 3) Igneous rocks on the islands of the Leeward Antilles arc, Aruba to Los Testigos, show a steady decrease in age from west to east (94.7-37.4 Ma), suggesting that the islands have been progressively captured from the Antilles arc by the plate boundary during the prolonged island arc-continent collision. Terrane capture models thus far cannot completely explain the data. 4) High (> 6.5 km/s) P-velocity bodies are found in the shallow crust along the main strike-slip faults along much of the plate boundary. We interpret these as elements of the HP/LT metamorphic terranes found in the adjacent thrust belts of central Venezuela. This suggests to us that displacement partitioning in the trench and subsequent strike-slip both play important roles in exhumation of the HP/LT terranes. 5) Crustal thickness variations in the plate boundary region are large (> 10 km), of short spatial wavelength (< 100 km), and indicate that the highest elevations of the coastal mountain belts are not supported isostatically.
Levander, A.; Schmitz, M.; Working Groups, B.
The Rivera-Cocos Plate Boundary Revisited
NASA Astrophysics Data System (ADS)
The nature of the boundary between the Rivera and Cocos plates has long been controversial. Early studies (predominantly earthquake studies) suggested that it was a NE oriented left lateral transform boundary. With the collection of multi-beam bathymetric data during the SEAMAT cruise of the N/O Jean Charcot in 1987 it became clear that this early proposal was not entirely correct as no clear transform morphology was observed. Shortly after the SEAMAT campaign, three main proposals emerged to explain this lack of transform morphology. The first two proposals favored the results of earthquake studies over the new multibeam data. The first proposed that the boundary is indeed a left-lateral transform boundary, you just cannot see it. In other words, it was a diffuse boundary and the resolution of the multi-beam data was not sufficient to reveal the associated deformation. The second proposal was that it was an east-west oriented, dextral transform, the proposal being based on the results of an earthquake directivity analysis. The third proposal favored the morphologic data over the earthquake data and proposed that the plate boundary was not a transform boundary, but was instead a divergent boundary, at least near the Middle America Trench in what is now called the EL Gordo Graben. Implicit in this proposal was that the earthquake activity did not reflect plate motions but rather were the result of local stresses. Since 2002, several marine geophysical campaigns have been conducted in the area of the Rivera-Cocos plate boundary with the aim of resolving this debate. During the 2002 BART and FAMEX campaigns of the N/O L'ATALANTE, multibeam bathymetric and seafloor backscatter data were collected along the boundary. During the MARTIC04 and MARTIC05 campaigns of the B/O EL PUMA dense total field magnetic surveys were conducted covering the entire plate boundary. Lastly, the multibeam coverage obtained during the BART/FAMEX campaigns was extended northward during the MORTIC07 campaign of the B/O EL PUMA. In this talk we will present these new data (some of which have already been published) and discuss the constraints that these data impose on the nature of the Rivera-Cocos plate boundary.
Bandy, W. L.; Mortera-Gutierrez, C. A.; Michaud, F.; Ortega Ram�rez, J.
Active faults, stress field and plate motion along the Indo-Eurasian plate boundary
NASA Astrophysics Data System (ADS)
The active faults of the Himalayas and neighboring areas are direct indicators of Recent and sub-Recent crustal movements due to continental collision between the Indian and Eurasian plates. The direction of the maximum horizontal shortening or horizontal compressive stress axes deduced from the strike and type of active faulting reveals a characteristic regional stress field along the colliding boundary. The trajectories of the stress axes along the transcurrent faults and the Eastern Himalayan Front, are approximately N-S, parallel to the relative motion of the two plates. However, along the southern margin of the Eurasian plate, they are NE-SW in the Western Himalayan Front and NW-SE to E-W in the Kirthar-Sulaiman Front, which is not consistent with the direction of relative plate motion. A simple model is proposed in order to explain the regional stress pattern. In this model, the tectonic sliver between the transcurrent faults and the plate margin, is dragged northward by the oblique convergence of the Indian plate. Thus, the direction of relative motion between the tectonic sliver and the Indian plate changes regionally, causing local compressive stress fields. Judging from the long-term slip rates along the active faults, the relative motion between the Indian and Eurasian plates absorbed in the colliding zone is about one fourth of its total amount; the rest may be consumed along the extensive strike-slip faults in Tibet and China.
Nakata, Takashi; Otsuki, Kenshiro; Khan, S. H.
Viscoelastic deformation near active plate boundaries
NASA Technical Reports Server (NTRS)
Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.
Ward, S. N.
Absolute Plate Motions by Boundary Velocity Minimizations
The main interaction of the interior with the lithosphere is as a material source and sink. An absolute reference frame defined by minimizing the translational motion of tectonic plate boundaries differs by 0.6 cm\\/yr from a frame defined by hot spo_t traces and by 0.4 cm\\/yr from the frame defined by the most plausible model of drag forces on the
William M. Kaula
On boundary controllability of a vibrating plate
A vibrating plate is here taken to satisfy the model equation:utt + ?2u = 0 (where?2u:= ?(?u); ? = Laplacian) with boundary conditions of the form:uv = 0 and(?u)v = ? = control. Thus, the state is the pair [u, ut] and controllability means existence of? on S:= (0,T)�?O transfering �any�[u, ut]0 to �any�[u, ut]T. The formulation is given by
Werner Krabs; G�nter Leugering; Thomas I. Seidman
Convergent plate margin east of North Island, New Zealand
The Indian-Pacific plate boundary passes along the eastern margin of North Island, New Zealand, with the Pacific plate being thrust under the Indian plate to the west. The continental slope forming the Indian plate margin is broad with a well-formed series of trench slope basins and intervening ridges along the continental slope and shelf, subparallel to the margin, and continuing onto land. Multichannel seismic reflection data recorded across this margin show a thick (2.5-km) sedimentary section overlying oceanic basement in the deep-water part of the profile, and part of this sedimentary section is apparently being subducted under the accretionary prism. At the toe of the continental slope, nascent thrusts, often showing little apparent offset but a change in reflection amplitude, occur over a broad region. Well-defined trench slope basins show several episodes of basin formation and thrusting and are similar to structural interpretations for adjacent onshore basins. A bottom simulating reflector, which may delineate a gas-hydrate layer, can be traced over the midslope part of the profile. A major reflector, interpreted as the base of the accretionary prism, can be traced discontinuously to the coast where it coincides with the top of a zone of high seismicity, considered to mark the top of the subducted Pacific plate.
Davey, F.J; Hampton, M.; Lewis, K.
A new plate boundary in the Ionian Sea
NASA Astrophysics Data System (ADS)
The Calabrian Arc (CA) is a narrow and arcuate subduction system resulting from Africa/Eurasia plate convergence and slab rollback in the Tyrrhenian region. The very slow present-day plate convergence suggests a decrease in subduction efficiency, but underplating may still be active in the central CA where GPS data suggests an outward motion of Calabria relative to Apulia. Shortening in the accretionary wedge is taken up along the outer deformation front and out-of-sequence thrust faults (splay faults). Transtensive deformation accounts for margin segmentation along transfer tectonics systems bounding different margin segments. Transfer faults represent the shallow expression of deeply rooted processes at the slab edge. One of these structures is the NNW-SSE trending transtensive STEP (Slab Transfer Edge Propagator) fault system located East of the Malta Escarpment from the Alfeo seamount to the Etna volcano. Margin segmentation occurs along a second NW-SE trending crustal discontinuity delimiting two distinct lobes of the subduction complex close to the Messina Straits region. The Western Lobe (WL) of the subduction complex, offshore Sicily, is a down-dropped and very low tapered (about 1.5� ) wedge detaching on the base of the Messinian evaporites. The Eastern Lobe (EL), in front of Central Calabria, shows a more elevated accretionary wedge, steeper topographic slopes, higher deformation rates and a deeper basal detachment. High resolution tomographic images suggest a strong interplay between structural development and slab dynamics: the WL corresponds to areas where the slab is detached, while beneath the EL the slab is continuous. Newly acquired geophysical data (Urania cruise, October 2013), reveal that the deformation zone between the two lobes of the accretionary wedge displays fresh seafloor scarps and mud volcanoes suggesting it represents an active tectonic boundary and a deep fluid/mud conduit. We propose that this discontinuity is a new plate boundary segment in the Ionian Sea, connecting the compressive belt in northern Sicily to the Hellenic Arc system and dissecting the CA subduction complex. This deformation zone accommodates differential movements of the Calabrian and the Peloritan portions of CA and can explain the NW-SE extension observed in the straits of Messina as well as the relative motion between Calabria and NE Sicily. This reconstruction is in agreement with geodetic data and earthquake slip vectors observations which suggest the existence of a microplate in the central Mediterranean. The discontinuity between the two lobes would thus represent a major component of the southwestern (hitherto poorly constrained) boundary of this microplate. The motion of Africa relative to Eurasia would be accommodated along this structure by relative rotations between the different blocks resulting from African plate fragmentation.
Polonia, Alina; Torelli, Luigi; Artoni, Andrea; Bortoluzzi, Giovanni; Faccenna, Claudio; Ferranti, Luigi; Gasperini, Luca; Govers, Rob; Monaco, Carmelo; Neri, Giancarlo; Orecchio, Barbara; Rinus Wortel, M. J.
Origin of production gases from convergent plate margins
Molecular and isotopic composition of hydrocarbon production gases from four convergent plate margins have been measured. New Zealand is represented by two gases from the Taranaki basin in the back arc of the active Tonga-Kermadec subduction system. Gases from Barbados and Taiwan are from forearc locations in the active Lesser Antilles system and relict northern Manila Trench system. Philippine gases from offshore Palawan are associated with the Palawan Trough. Gases from Taiwan, the Maiu field in New Zealand, and the Nido field in Palawan have very high /sup 3/He//sup 4/He ratios, indicating considerable mantle input of helium to the gas reservoirs. Variations in /sup 3/He//sup 4/He ratios in neighboring fields are quite striking and suggest localized sources for the mantle components. Possible sources include shallow igneous bodies and fractures or faults tapping a direct mantle source. Measurements of helium isotope ratios in hydrocarbon production gases have been compiled and show a striking association of mantle helium with gases from subduction zones in contrast to deep subsided or rifted sedimentary basins. The dynamics of the subduction process, involving the interaction of upper mantle and crustal rocks, is apparently responsible for the injection of volatile mantle components into reservoired gases. Current exploration techniques are based on maturation and gas migration theories developed from the study of subsiding sedimentary basins. At convergent margins, such technique may have to be amended to include the effects of subduction dynamics on the source, maturation, and migration of hydrocarbons.
Jeffrey, A.W.A.; Poreda, R.J.; Gwilliam, W.J.; Kaplan, I.R.; Craig, H.
On a boundary layer phenomenon in Mindlin-Reissner plate theory for laminated circular sector plates
Summary In this article, the edge-zone equation of Mindlin-Reissner plate theory, for composite plates laminated of transversely isotropic layers is studied. Analytical solutions are obtained for both circular sector and completely circular plates with various boundary conditions. The boundary-layer function and its effect on the stresses are numerically studied. Effects of plate thickness and boundary conditions are investigated. The results
A. Nosier; A. Yavari; S. Sarkani
The Plate Boundary Observatory: Operational Status and Data Plans
The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. The science goals of PBO require that plate boundary deformation be adequately characterized over the wide range of spatial and
G. Anderson; K. Feaux; M. Jackson; W. Prescott
Prototypical Concepts and Misconceptions of Plate Tectonic Boundaries
NASA Astrophysics Data System (ADS)
Students of geology encounter many prototypical/exemplar concepts* that include representative, but not necessarily defining, features and characteristics. This study of students' prototypical representations of plate tectonic boundaries indicates that their representations are rich sources of information about their misconceptions about plate tectonics. After lectures in plate tectonics and mountain building, 353 students in a general education geology class were asked to draw a continent-continent convergent boundary. For this study, a correct answer is defined as having the major features in correct proportions as depicted in the plate boundary diagrams on the USGS web. Fifty-two percent of the drawings were either incorrect or incomplete such that they could not be interpreted. Only 48% were readily interpretable, and of these 22% drew the boundary correctly, showing a thickening of crust where two continents collide. Thirty-three percent drew the boundary showing concave slabs of continental crust as one might imagine two pieces of firm rubber pushed together on a rigid surface and 45% depicted mountains as one might imagine inverted ice cream cones on a rigid plank. Twenty-one senior class geology majors and graduate students were given the same assignment. Forty-eight percent rendered a correct drawing, whereas 38% drew the same ice cream cone on a plank type picture that 45% of the general education students drew. In a second class of 12 geology majors, only 1 student drew a cross section of a continent-ocean boundary similar to standard representation. Four of 12 drew mountains on the top of continental crust over a subduction zone but did not draw a compensating mass within the crust or lithosphere. Prototypical drawings provide more information about students' concepts than do most multiple-choice questions. For example, sixty-two percent of theses students who drew mountains similar to foam rubber pads pushed together on a desk or ice cream cones on a plank correctly answered a multiple-choice question that would appear to indicate a better understanding than the drawings reveal. Furthermore, 12 interviewed students made statements that could be interpreted to indicate that they understood the concept of mountain building at plate tectonic boundaries better than their drawings suggest. Incoherence of multiple-choice responses, verbal statements and drawings may be common in novice learners. If cognitive scientists are correct in their model of multiple types of mental representations for the same term, then the fact that novices may hold inconsistent representations is not surprising. The fact that students at various academic levels draw very similar prototypes that are incorrect is evidence that students have distinct and persistent prototype misconceptions. * Cognitive scientists define a prototypical/exemplar concept as a mental representation of the best examples or central tendencies of a term.
Sibley, D. F.; Patino, L. C.
Convergence of adaptive BEM for some mixed boundary value problem
For a boundary integral formulation of the 2D Laplace equation with mixed boundary conditions, we consider an adaptive Galerkin BEM based on an (h?h/2)-type error estimator. We include the resolution of the Dirichlet, Neumann, and volume data into the adaptive algorithm. In particular, an implementation of the developed algorithm has only to deal with discrete integral operators. We prove that the proposed adaptive scheme leads to a sequence of discrete solutions, for which the corresponding error estimators tend to zero. Under a saturation assumption for the non-perturbed problem which is observed empirically, the sequence of discrete solutions thus converges to the exact solution in the energy norm.
Aurada, M.; Ferraz-Leite, S.; Goldenits, P.; Karkulik, M.; Mayr, M.; Praetorius, D.
Convergence of adaptive BEM for some mixed boundary value problem.
For a boundary integral formulation of the 2D Laplace equation with mixed boundary conditions, we consider an adaptive Galerkin BEM based on an [Formula: see text]-type error estimator. We include the resolution of the Dirichlet, Neumann, and volume data into the adaptive algorithm. In particular, an implementation of the developed algorithm has only to deal with discrete integral operators. We prove that the proposed adaptive scheme leads to a sequence of discrete solutions, for which the corresponding error estimators tend to zero. Under a saturation assumption for the non-perturbed problem which is observed empirically, the sequence of discrete solutions thus converges to the exact solution in the energy norm. PMID:23482570
Aurada, M; Ferraz-Leite, S; Goldenits, P; Karkulik, M; Mayr, M; Praetorius, D
The Plate Boundary Observatory: Data Management Progress and Highlights
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser
G. Anderson; B. Blackman; J. Eakins; K. Hodgkinson; J. Matykiewicz; F. Boler; M. Beldyk; B. Henderson; B. Hoyt; E. Lee; E. Persson; J. Smith; D. Torrez; J. Wright; M. Jackson; C. Meertens
Features on Venus generated by plate boundary processes
Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults
Dan McKenzie; Peter G. Ford; Catherine Johnson; Barry Parsons; David Sandwell; Stephen Saunders; Sean C. Solomon
Structures and kinematics in the northeastern Mediterranean: A study of an irregular plate boundary
NASA Astrophysics Data System (ADS)
Extensional structures are prominent in the northeastern Mediterranean, a unique sector of the Africa-Eurasia plate convergence zone. To explain this paradoxical situation, we analyse here the young tectonics of this region by examining its structural elements and plate kinematics. Offshore multichannel seismic reflection profiles and onland geology show that the stuctural settings are different on the two sides of the northeastern Mediterranean triple junction (AFR-ARB-ANA). On the east, stuctures controlled by strike-slip and by compression coexist, whereas on the west compression is not very conspicuous. Here, deep basins separated by a partly submerged ridge are prominent. We interpret the ridge, which comprises the Kyrenia- Misis-Andirin Unit at its core, as a large flower structure which extends from southeastern Turkey to Cyprus; the Adana-Cilicia and the Iskenderun-Latakia-Mesaoria Basins on its flanks are interpreted as due to extension. This interpretation agrees with the relative motions between the Africa, Arabia, Eurasia and Anatolia plates in this region. Analysis of the local plate kinematics reveals that strike-slip predominates along the southern boundary of the Anatolia plate in this region, as a result of Anatolia's westward escape. East of the triple junction this motion is associated with comparable shortening transverse to the plate boundary, whereas west of the triple junction the motion transverse to the plate boundary varies between slight compression to extension, depending mainly on the local strike of the plate boundaries. These variations, calculated from regional data, correlate well with the observed structural changes along the northeastern Mediterranean sector of the plate convergence zone. The structural-kinematic analysis explains both the lateral changes in the deformation style and the existence of local extension in the northeastern Mediterranean.
Kempler, Ditza; Garfunkel, Zvi
Convergence of Difference Methods for Initial and Boundary Value Problems with Discontinuous Data.
National Technical Information Service (NTIS)
The paper extends the classical convergence theory for numerical solutions to initial and boundary value problems with continuous data (the right-hand side) to problems with Riemann integrable data. Order of convergence results are also obtained. (Author)
B. A. Chartres R. S. Stepleman
Statistical tests of additional plate boundaries from plate motion inversions
The application of the F-ratio test, a standard statistical technique, to the results of relative plate motion inversions has been investigated. The method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance. This approach appears to be useful in
Seth Stein; R. G. Gordon
Partial and Complete Rupture of the Indo-Andaman Plate Boundary 1847-2004
We review seismicity along the Nicobar\\/Andaman plate boundary prior to the Mw=9 earthquake of 26 December 2004, with particular attention to reverse slip in the central and northern parts of the rupture zone 600-1300 km north from the epicenter. Slip is partitioned between convergence and strike-slip motion, which in the northern Andamans is assisted by back-arc spreading. Subduction zone earthquakes
R. Bilham; R. Engdahl; N. Feldl; S. P. Satyabala
Calibrated Plate Boundary Observatory Borehole Strainmeter Data
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), funded by NSF as part of the Earthscope program and installed and maintained by UNAVCO, includes 75 borehole strainmeters (BSMs), which makes it one of the largest strainmeter arrays in the world. Co-located with seismometers, and embedded within the PBO continuous GPS network, the strainmeters expand the bandwidth of the Observatory enabling the capture of signals with periods of days to minutes. Six years after installation of the first strainmeter, over 70% of the network is in compression and over 85% of the instruments have a strong signal to noise ratio in the M2 tidal band. UNAVCO's BSM engineers ensure the network usually collects over 95% percent of possible data. UNAVCO makes the BSM Level 0 (raw) and Level 2 (processed) data products available to the community via the Northern California Earthquake Data Center (NCEDC), the IRIS DMC and UNAVCO's own web site. Processed BSM data includes gauge, areal, differential and tensor shear strains plus data edits and time series corrections for barometric pressure, earth tides, ocean load and borehole trends. Before strain data can be incorporated into a geophysical model with confidence, however, an instrument response must be found that relates the gauge measurements to the regional strains (i.e., an in-situ calibration is needed). In this presentation we describe the method UNAVCO will use to calibrate PBO strainmeters using earth tides as a reference signal and assuming an anisotropic instrument setting. The calibrated data will be released in a simple delimited ASCII format and will be included with the processed data set that is currently updated every 24 hours. In addition to the 5-minute Level 2 data set, UNAVCO will include the calibrated areal and shear strains at 1-sps for significant events anywhere in the world as part of its Special Event series. In order to meet Earthscope goals of data transparency and processing repeatability, the expanded processed data sets will include a summary of the calibration method, tidal observations, predictions upon which the calibrations are based and the strain matrix used to generate the areal and shear data. This presentation will also describe the new file naming convention that will allow the user to 1.) select a preferred calibration method for their data and 2.) allow UNAVCO the flexibility of including new methods of calibration in the future.
Hodgkinson, K. M.; Mencin, D.; Borsa, A. A.; Fox, O.; Gallaher, W. W.; Gottlieb, M. H.; Henderson, D. B.; Johnson, W.; Pyatt, C.; Van Boskirk, L.
The Plate Boundary Observatory: Data Management Progress and Highlights
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 891 continuous GPS stations, up to 174 borehole strainmeter stations, and five laser strainmeters,
G. Anderson; K. Hodgkinson; M. Jackson; J. Wright
The Plate Boundary Observatory: Data Management Progress and Highlights
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters,
G. Anderson; J. Eakins; K. Hodgkinson; J. Matykiewicz; F. Boler; M. Beldyk; B. Hoyt; E. Lee; E. Persson; D. Torrez; J. Wright; M. Jackson; W. Prescott
Active Faulting in the Ninetyeast Ridge and Implications for Diffuse Plate Boundaries of the Indo-Australian Plate
NASA Astrophysics Data System (ADS)
The Ninetyeast Ridge (NER) in the central Indian Ocean is within a zone of diffuse deformation where the Indo-Australian plate is fracturing into three smaller plates (India, Capricorn, Australia). Deformation style appears to change across the NER and parts of the ridge are seismically active, suggesting that it holds clues about the diffuse plate boundaries. Seismic profiles collected along the NER image faults that show different styles of deformation along the length of the ridge. The northern NER (0-5�N) displays transpression along nearly east-west faults, likely a result of compression between India and Australia that is oblique to the NER. The observed faults explain the poorly understood distribution of earthquakes that occurred in April 2012 south of Sumatra. In the central NER (5-8�S), intense deformation results from nearly north-south compression, either from convergence of India and Capricorn or India and Australia. In contrast, deformation is slight and extensional in nature in the southern NER (10-27�S), which has little seismic activity. This deformation is inconsistent with predicted relative motions along much of the southern NER, implying that it is not a part of a plate boundary. Instead, we suggest that motion between the Capricorn and Australian plates follows ancient fracture zones east of the NER. At all sites, faulting appears controlled by the reactivation of original crustal faults, either normal faults formed by seafloor spreading or fracture zones, implying that diffuse deformation is opportunistic and is focused along existing zones of weakness.
Sager, W. W.; Bull, J. M.; Krishna, K. S.
A new dynamic model of divergent plate boundary
The dynamics of divergent plate boundary, including continent rift and mid-oceanic ridge, is insufficiently understood. A new dynamic model is presented in this paper, which describes the motion of plate evolving continuously in space and time. The model is based on the three-dimensional Navier-Stokes equation with Boussinesq approximation. Two significant terms are added to the model to describe the plate
C. Yu
Diffuse interseismic deformation across the Pacific North America plate boundary
Crustal movements and deformation within the diffuse Pacific North America (Pa-NA) plate boundary are dominated by the right-lateral motion between the two plates. By using the Pa-NA pole of rotation (PoR) spherical coordinate system, we decompose observed crustal movements into parallel and normal components to the Pa-NA plate motion. We transformed the 840 velocity vectors of the Southern California Earthquake
Shimon Wdowinski; Bridget Smith-Konter; Yehuda Bock; David Sandwell
Tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip
NASA Astrophysics Data System (ADS)
At subduction zones, convergence between the two plates at shallow levels was thought to occur aseismically, accommodated by asiesmic slip along either the megathrust plate boundary or splay faults that branch upwards at high angles into a wedge of overlying sediment. However, some anomalous, enigmatic events are known to occur infrequently in this region, including tsunami earthquakes that generate tsunamis disproportionately large for their seismic energy, and very-low-frequency earthquakes. Here we report close-in observations of very-low-frequency earthquakes, measured using broadband ocean-bottom seismometers, occurring at the shallowest parts of the plate boundary at the Nankai Trough. We find that the very-low-frequency events are generated by slip on extremely low-angle thrust faults along the plate boundary beneath the sedimentary wedge. The earthquakes have durations of 30-100s, anomalously long when compared with the 1-2s duration of ordinary earthquakes with comparable magnitudes of Mw 3.8-4.9 (ref. ). Despite their slowness, the waves are unexpectedly rich in high-frequency components, a feature consistent with shear failure driven by tectonic stress and fluid-pressure-controlled tensile fractures. The occurrence of this slow, yet seismic slip implies that the shallowest part of the plate boundary could be a source of tsunami earthquakes.
Sugioka, Hiroko; Okamoto, Taro; Nakamura, Takeshi; Ishihara, Yasushi; Ito, Aki; Obana, Koichiro; Kinoshita, Masataka; Nakahigashi, Kazuo; Shinohara, Masanao; Fukao, Yoshio
The Okhotsk Plate and the Eurasia-North America plate boundary zone.
NASA Astrophysics Data System (ADS)
The Eurasia-North America plate boundary zone transitions from spreading at rates of ~ 25mm/yr in the North Atlantic, to compression at rates of ~ 5mm/yr in the region of the Okhotsk plate. Because the pole of rotation between Eurasia and North America lies more or less on their mutual boundary, there is a linear change in rate along the boundary, and regions near the euler pole are subject to extremely low deformation rates. The Okhotsk - Eurasia - North America triple junction lies slightly south of the rotation pole, placing the Okhotsk plate entirely in a weakly contractional setting. Regions near the triple junction absorb 1mm/yr contraction. Further south, towards the shoreline of the Okhotsk sea, up to 5 mm/yr contraction may be absorbed within the plate. How shortening is accommodated across the boundary remains an open question. One possibility is wholesale extrusion of the entire Okhotsk plate (or possibly its northwestern corner) along two plate boundary strike slip faults (Eurasia-Okhostk and North America Okhotsk). The problem with this model is that the seismic record does not presently clearly support it, with the largest events distributed both within the plate interior and on its boundaries. This may suggest that instead, the Okhotsk plate, and particularly its north-western end, consists of a series of smaller blocks which shuffle against each other, partially accommodating extrusion, but also permitting some internal deformation and change of shape of the Okhotsk plate itself. We present analyses of the very sparse seismic record from the region, as well as geometric-kinematic, tectonic models of the possible deformation of northwest Okhotsk to try to better understand the different probabilities of how this slowly deforming plate boundary zone is behaving.
Hindle, David; Mackey, Kevin
The accommodation of Arabia-Eurasia plate convergence in Iran
Continental convergence between Arabia and Eurasia is taken up by distributed deformation in Iran. At wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field. The only quantitative source of information on the spatial distribution of strain rates within Iran is the record of earthquakes. We find that we can reproduce
James Jackson; John Haines; William Holt
Plate convergence, transcurrent faults and internal deformation adjacent to Southeast Asia and the western Pacific
NASA Technical Reports Server (NTRS)
A model for oblique convergence between plates of lithosphere is proposed in which at least a fraction of slip parallel to the plate margin results in transcurrent movements on a nearly vertical fault which is located on the continental side of a zone of plate consumption. In an extreme case of complete decoupling only the component of slip normal to the plate margin can be inferred from underthrusting. Recent movements in the western Sunda region provide the most convincing evidence for decoupling of slip, which in this region is thought to be oblique to the plate margin. A speculative model for convergence along the margins of the Philippine Sea is constructed from an inferred direction of oblique slip in the Philippine region. This model requires that the triple point formed by the junction of the Japanese and Izu-Bonin trenches and the Nankai trough migrate along the Sagami trough.
Fitch, T. J.
A diffuse plate boundary model for Indian Ocean tectonics
NASA Technical Reports Server (NTRS)
It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.
Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.
Fluid budgets at convergent plate margins: Implications for the extent and duration of fault-zone dilation
Faults at convergent plate boundaries are important conduits for fluid escape, and recent evidence suggests that fluid expulsion along them is both transient and heterogeneous. For the Nankai and Barbados convergent margins, we have used numerical models to investigate the long-term partitioning of expelled fluids between diffuse flow and flow along connected high-permeability fault conduits. For a simple case of spatial heterogeneity, we estimated the extent of high-permeability conduits necessary to maintain a balance between incoming and expelled fluids. For the case of transient expulsion, we constrained the duration of elevated permeability required to balance the fluid budgets. Comparison of modeled and observed geochemical profiles suggests that the initiation of connected flow conduits is delayed with respect to the time of accretion into each accretionary complex and may be related to burial below a critical depth, either where the overlying wedge is sufficiently thick to prevent fluid escape to the sea floor or where sediments behave brittlely.
Saffer, D. M.; Bekins, B. A.
Preliminary estimates of plate convergence in the Caucasus collision zone from global positioning system measurements
Global Positioning System (GPS) measurements (1991-1994) traversing the Greater and Lesser Caucasus mountains indicate a minimum N-S shortening of 10+\\/-2mm\\/yr. This represents approximately 30-50% of the NUVEL-1A convergence rate between the Arabian and Eurasian plates. The remainder of the convergence appears to be accommodated in the areas south of the Lesser Caucasus, by a combination of right-lateral strike-slip faulting on
R. E. Reilinger; S. C. McClusky; B. J. Souter; M. W. Hamburger; M. T. Prilepin; A. Mishin; T. Guseva; S. Balassanian
A great earthquake rupture across a rapidly evolving three-plate boundary.
On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis. PMID:19359581
Furlong, Kevin P; Lay, Thorne; Ammon, Charles J
Iberian plate kinematics: A jumping plate boundary between Eurasia and Africa
THE rotation of Iberia and its relation to the formation of the Pyrenees has been difficult to decipher because of the lack of detailed sea-floor spreading data, although several models have been proposed1-7. Here we use detailed aeromagnetic measurements from the sea floor offshore of the Grand Banks of Newfoundland to show that Iberia moved as part of the African plate from late Cretaceous to mid-Eocene time, with a plate boundary extending westward from the Bay of Biscay. When motion along this boundary ceased, a boundary linking extension in the King's Trough to compression along the Pyrenees came into existence. Finally, since the late Oligocene, Iberia has been part of the Eurasian plate, with the boundary between Eurasia and Africa situated along the Azores-Gibraltar fracture zone.
Srivastava, S. P.; Schouten, H.; Roest, W. R.; Klitgord, K. D.; Kovacs, L. C.; Verhoef, J.; Macnab, R.
In-Plane Vibration Analysis of Annular Plates with Arbitrary Boundary Conditions
In comparison with the out-of-plane vibrations of annular plates, far less attention has been paid to the in-plane vibrations which may also play a vital important role in affecting the sound radiation from and power flows in a built-up structure. In this investigation, a generalized Fourier series method is proposed for the in-plane vibration analysis of annular plates with arbitrary boundary conditions along each of its edges. Regardless of the boundary conditions, the in-plane displacement fields are invariantly expressed as a new form of trigonometric series expansions with a drastically improved convergence as compared with the conventional Fourier series. All the unknown expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz technique. Unlike most of the existing studies, the presented method can be readily and universally applied to a wide spectrum of in-plane vibration problems involving different boundary conditions, varying material, and geometric properties with no need of modifying the basic functions or adapting solution procedures. Several numerical examples are presented to demonstrate the effectiveness and reliability of the current solution for predicting the in-plane vibration characteristics of annular plates subjected to different boundary conditions.
Qin, Zhengrong; Wang, Qingshan
An EarthScope Plate Boundary Observatory Progress Report
UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest
M. Jackson; G. Anderson; F. Blume; C. Walls; B. Coyle; K. Feaux; B. Friesen; D. Phillips; K. Hafner; W. Johnson; D. Mencin; B. Pauk; T. Dittmann
Plate convergence along the northern Manila Trench, Taiwan-Luzon region
NASA Astrophysics Data System (ADS)
The Philippine Sea Plate overrides the Eurasian Plate along the east-dipping Manila Trench. From Luzon to Taiwan, the plate convergence evolves gradually from normal subduction to collision. Further north, the Taiwan orogen has been created. As evidenced by the earthquakes, the subduction-related earthquakes become diffusive close to Taiwan. The accretionary prism has also become wider toward Taiwan. To understand the transition of the plate convergence, we have collected 6 reflection seismic profiles across the Manila Trench between Luzon and Taiwan. The results show that the basement generally displays larger dipping angle in the south than in the north. The trench-fill sediments near the trench have larger quantity in the south than in the north. In the north, the trench-fill sediments have even been uplifted. Structural analysis shows that the crustal structures close to the trench area can be divided into two distinctive sub-areas: the normal fault zone and the proto-thrust zone. The normal fault zone is characterized by the distribution of numerous normal faults in the upper layer of the bent subducting plate. When the normal faults approache the trench, they are generally covered by trench-fill sediments. It implies that the normal faults occur at a maximum bending moment of the plate. Some normal faults resumes probably due to the strong plate convergence near the accretionary prism. The proto-thrust zone is located between the normal fault zone and the frontal thrust of the accretionary prism. Proto-thrust zone contains numerous blind-thrust beneath the trench area. The observation of the proto-thrust zone suggests two tectonic insights. Firstly, the compression of plate convergence comes from the base of the decollement and propagates upwards. Alternatively, the blind-thrusts come from the inheritance of the subducting normal faults.
Ku, C.; Hsu, S.
Bolivar: Crustal Structure of the Caribbean-South America plate boundary at 70W
NASA Astrophysics Data System (ADS)
The Caribbean-South America plate boundary is characterized by tectonic transpression with oblique convergence. The ~ 20 mm/yr eastward displacement of the Caribbean plate, with respect to a fixed South America causes the plate boundary to have a dominant right-lateral strike-slip component, accommodated by the San Sebastian-El Pilar fault system. To the west, relative plate motion is complicated by the northeastward tectonic escape of the Maracaibo block along the Bocono and Santa Marta strike-slip faults, and the shortening between North and South America. The convergence rate between the Maracaibo block and the Caribbean has been estimated to be ~ 2 mm/yr. The multidisciplinary BOLIVAR project seeks to understand the complex plate interaction of the Caribbean- South American diffuse plate boundary. We hypothesize that this may be a site of continental growth by island arc accretion of the Leeward Antilles onto South America. The active-seismic component of the project, completed in June 2004, concentrated along five main onshore-offshore profiles extending from the Caribbean basin to the front of the fold and thrust belts of Venezuela. Seismic refraction data were acquired as well as coincident multi-channel seismic (MCS) lines in the offshore sections. We present results from seismic reflection and wide-angle refraction data along a 450 km-long onshore- offshore north-south striking profile at 70 degrees west longitude. Refraction data were used to develop 2-D velocity models from independent and simultaneous traveltime inversion of first arrivals and PmP reflections from 40 Ocean Bottom Seismometers (OBS) and about ~ 80 land recorders. A coincident MCS profile was processed and interpreted independently. Offshore western Venezuela the Caribbean plate is anomalously thick ~ 15 km. The velocity model from wide-angle data is well correlated with the structures interpreted in the reflection data; in particular in the upper and middle crust of the Southern Caribbean Deformed Belt, the Falcon Basin and the Aruba Rise. High- velocity anomalies are spatially associated with the strike-slip Oca-Ancon fault in the region. Underthrusting of the Caribbean plate beneath the South America plate is inferred from the presence of low velocity sediments beneath the South Caribbean Deformed Belt over a distance of 75-100 km.
Guedez, M. C.; Zelt, C. A.; Magnani, B. M.; Levander, A.
Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)
NASA Astrophysics Data System (ADS)
Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.
Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.
Initiation of plate boundary slip in the Nankai Trough off the Muroto peninsula, southwest Japan
NASA Astrophysics Data System (ADS)
To investigate variations in physical properties accompanying the development of the d�collement, we used a neural network analysis of seismic attributes derived from 3D seismic reflection data gathered in the Nankai Trough convergent margin off the Muroto peninsula of southwest Japan. This analysis resulted in a detailed map of the geological features along the d�collement and revealed a drastic change in physical properties at the sole of the proto-thrust. Ocean Drilling Program (ODP) data suggest that the d�collement physical property change coincides with the initiation of slip. Furthermore, changes in the structure of the accretionary prism and reorganization of the d�collement geometry also attend the initiation of plate boundary slip.
Tsuji, Takeshi; Matsuoka, Toshifumi; Yamada, Yasuhiro; Nakamura, Yasuyuki; Ashi, Juichiro; Tokuyama, Hidekazu; Kuramoto, Shin'ichi; Bangs, Nathan L.
Modeling the Philippine Mobile Belt: Tectonic blocks in a deforming plate boundary zone
NASA Astrophysics Data System (ADS)
The Philippine Mobile Belt, a seismically active, rapidly deforming plate boundary zone situated along the convergent Philippine Sea/Eurasian plate boundary, is examined using geodetic and seismological data. Oblique convergence between the Philippine Sea Plate and the Eurasian plate is accommodated by nearly orthogonal subduction along the Philippine Trench and the Manila Trench, as well as by strike-slip faulting along the Philippine Fault system. We develop a model of active plate boundary deformation in this region, using elastic block models constrained by known fault geometries, published GPS observations and focal mechanism solutions. We then present an estimate of block rotations, fault coupling, and intra-block deformation, based on the best-fit model that minimizes the misfit between observed and predicted geodetic vectors and earthquake slip vectors. Slip rates along the Philippine fault vary from ~22 - 36 mm/yr in the Central Visayas and about 10 to 40 mm/yr in Luzon, trending almost parallel to the fault trace. In northern Luzon, Philippine Fault splays accommodate transpressional strain. The Central Visayas block experiences convergence with the Sundaland block along the Negros Trench and the Mindoro-Palawan collision zone. On the eastern side of Central Visayas, sinistral strike-slip faulting occurs along the NNW-SSE-trending Philippine Fault. Mindanao Island in southern Philippines is dominated by east-verging subduction along the Cotabato Trench, and strain partitioning (strike- slip faulting with west-verging subduction) in eastern Mindanao along the southern Philippine Fault and Philippine Trench, respectively. Oblique active sinistral strike slip faults in Central and Eastern Mindanao that were hypothesized to be responsible for basin formation are obvious boundaries for tectonic blocks. Located south of Mindanao Island we define an adjoining oceanic block defined by the N-S trending complex dual subduction zone of Sangihe and Halmahera, primarily delineated by seismicity, bathymetric profiles and E-W thrust mechanisms. In our preferred model, the Philippine Mobile Belt can be represented by at least 12 independently moving rigid tectonic blocks, separated by active faults and subduction zones.
Galgana, G. A.; Hamburger, M. W.; McCaffrey, R.; Bacolcol, T. C.; Aurelio, M. A.
Global positioning system measurements of Indian plate motion and convergence across the Lesser Himalaya
We use Global Positioning System (GPS) measurements acquired from 1991 to 1995 to constrain the motion of sites in Bangalore, in southern India, and Kathmandu, Nepal, relative to a global GPS network. These measurements permit estimates of the northward motion of the Indian plate and convergence between the southern Himalaya and the Indian subcontinent. The velocities of Bangalore and Kathmandu
J. Freymueller; R. Bilham; R. B�rgmann; K. M. Larson; J. Paul; S. Jade; V. Gaur
Comparisons of Numerical Simulations of Mantle Flow and Seismic Anisotropy in a Model Including a Plate Boundary Transition Region From Subduction to Transform to Subduction
The Caribbean-South American plate boundary zone is the result of an eastwardly-diachronous (time transgressive) arc-continent collision ocurring over the last 50 million years. The boundary consists of a long right-lateral transpressional zone with trenches of opposite polarity at either end. A similar situation is currently occuring in New Zealand where the oblique convergence between the Pacific and the Australian plates
L. T. Pinero; J. Lowman; J. Kendall
Discovering plate boundaries: Laboratory and classroom exercises using geodetic data to develop students' understanding of plate motion
To introduce the concept of plate boundaries, typical introductory geology exercises include students observing and plotting the location of earthquakes and volcanoes on a map to visually demarcate plate boundaries. Accompanying these exercises, students are often exposed to animations depicting the movement of Earth's tectonic plates over time. Both of these teaching techniques are very useful for describing where the
S. E. Olds
Boundary element method for 3-D cracks in a plate
NASA Technical Reports Server (NTRS)
Fundamental solutions which automatically satisfy boundary conditions at the interfaces of an elastic plate perfectly bonded to two elastic halfspaces are implemented in a three-dimensional BEM for crack problems. The BEM features a new integration scheme for highly singular kernels. The capability is achieved through a part analytic and part numerical integration procedure, such that the analytic part of the integration is similar for all slip/opening variations. Part-through elliptic cracks in an elastic plate with traction-free surfaces are analyzed and the SIF values along the crack front are found to compare favorably with the numerical SIF results of Raju and Newman (1979).
Fares, N.; Li, V. C.
Accuracy and convergence of a finite element algorithm for laminar boundary layer flow
NASA Technical Reports Server (NTRS)
The Galerkin-weighted residuals formulation is employed to derive an implicit finite element solution algorithm for a generally non-linear initial-boundary value problem. Solution accuracy and convergence with discretization refinement are quantized in several error norms, for the non-linear parabolic partial differential equation system governing laminar boundary layer flow, using linear, quadratic and cubic functions. Richardson extrapolation is used to isolate integration truncation error in all norms, and Newton iteration is employed for all equation solutions performed in double-precision. The mathematical theory supporting accuracy and convergence concepts for linear elliptic equations appears extensible to the non-linear equations characteristic of laminar boundary layer flow.
Soliman, M. O.; Baker, A. J.
TTR triple junction evolution during plate convergence in the southern branch of the european variscan orogen
NASA Astrophysics Data System (ADS)
The boundary between the Ossa-Morena and the South Portuguese zones (Iberian Massif) represents a major suture within the southern branch of the European Varis-can orogen. This suture resulted from the collision between the northern Iberian autochthon and the South Portuguese allochthon, and it is outlined by a WNW-ESE oriented, high grade band (the Aracena metamorphic belt, AMB). The main characteristics of the AMB are (1) the presence of a linear belt of MORB derived metabasites which shows a HT/LP inverted metamorphic gradient (Castro et al., 1996). This metamorphic event shows an age gradient (Castro et al., 1999), in such a way that younger ages have been obtained towards the east. (2) The occur-rence of a UHT/LP metamorphic event, related to an extensional deformation phase, affecting the former continental margin of the Iberian autochthon. (3) The existence of syn-to-post-tectonic noritic intrusions with boninite affinity composition, related to partial melting of a shallow mantle wedge (Castro et al., 1996). According to the mentioned characteristics the following tectonic model is pro-posed: (1) During the convergence between the Iberian autochthon and the South Portuguese allochthon, an oceanic ridge intersected the subduction zone giving place to a TTR triple junction, related to which a slab-free window formed and a thermal rebound took place. This triple junction migrated along the continental edge of the Iberian autochthon towards the east, generating a high-grade metamorphic belt (the AMB). (3) As the trailing oceanic plate subducted beneath the continental margin, it was heated up by the latter. In consequence, the upper levels of the oceanic sheet became dehydrated and were accreted to the base of the continental margin. The subduction plane migrated downwards and the oceanic metabasites together with the continental margin overthrusted the rest of the oceanic plate and the accretionary prism. (4) Once the trailing oceanic plate was totally consumed, a continental colli-sion occurred between the South Portuguese allochthon and the Iberian autochthon. Castro, A., Fern�ndez, C., de la Rosa, J.D., Moreno-Ventas, I., Rogers, G. (1996) Journal of Petrology, 37, 235-260. Castro, A., Fern�ndez, C., El-Hmidi, H., El-Biad, M., D�az, M., de la Rosa, J.D., Stuart, F. (1999) International Journal of Earth Sciences, 88, 26-37.
Diaz, M.; Fernandez, C.; Castro, A.
Initiation of deep convection along boundary layer convergence lines in a semitropical environment
The initiation of deep convection through forcing along boundary layer convergence lines is examined using observations from the Convection and Precipitation/Electrification (CaPE) Experiment conducted in east-central Florida during the summer of 1991. The study is concerned with the evolution and interaction of two converging air masses that were initially separated by an intervening boundary layer characterized by neutral stability and horizontal convective rolls. As anticipated, major thunderstorms erupt when the east coast breeze eventually collides with thunderstorm outflows from the west, but unexpected convection takes place prior to their merger along a well-defined confluence zone associated with a persistent quasi-stationary roll vortex signature. In this study, complementary interactions between roll vortex convergence lines and the sea-breeze front are not sufficient to trigger deep convection. However, organized convergence along the eastward-spreading thunderstorm outflows did interact periodically with roll vortex convergence maxima to initiate a new series of new storms. Results from two-dimensional numerical model simulations replicate many of the observed boundary layer features. Surface heating produces circulations similar to sea-breeze frontal zones that appear near the coastlines and progress steadily toward each other as the interior boundary layer deepens. Vertical velocity maxima develop over the associated convergence zones, but weaker periodic maxima also occur within the interior air mass at intervals similar to the spacing of observed horizontal roll vortices.
Fankhauser, J.C.; Crook, N.A.; Tuttle, J.; Miller, L.J.; Wade, C.G. [NCAR, Boulder, CO (United States)] [NCAR, Boulder, CO (United States)
Sonic imaging reveals new plate boundary structures offshore New Zealand
NASA Astrophysics Data System (ADS)
Recent bathymetry and sonar imagery studies of offshore portions of the plate boundary transecting New Zealand allow the first confident mapping of detailed tectonic and sedimentary patterns of the region. Working in late 1993 aboard the R/V L'Atalante of the Institut Francais de Recherche pour l' Exploitation de la Mer (IFREMER), we recorded soundings of a wide swath of seabed to elucidate major structural transitions along the plate boundary. Results of the study, part of the GEODYNZ-SUD program developed jointly by institutions in France and New Zealand, will be complemented by New Zealand cruises to the Puysegur and Hikurangi margins. The total data set will be processed and interpreted during the next two years.
Collot, J.-Y.; Delteil, J.; Herzer, R. H.; Wood, R.; Lewis, K.
A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons
We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding\\/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the
G. M Stampfli; G. D. Borel
Tectonics of the Nazca-Antarctic plate boundary
NASA Technical Reports Server (NTRS)
A new bathymetric chart of part of the Chile transform system is constructed, based mainly on an R/V Endeavor survey from 100 deg W to its intersection with the East Ridge of the Juan Fernandez microplate. A generally continuous lineated trend can be followed through the entire region, with the transform valley being relatively narrow and well-defined from 109 deg W to approximately 104 deg 30 min W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104 deg and 102 deg W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate-motion data from the eastern portion of the boundary, produce a new best-fit Euler pole for the Nazca-Antarctic plate pair, providing tighter constraints on the relative plate motions.
Anderson-Fontana, Sandra; Larson, Roger L.; Engeln, Joseph F.; Lundgren, Paul; Stein, Seth
Imprints of weak lithospheric plate boundaries in the observed geoid.
NASA Astrophysics Data System (ADS)
The observed geoid is highly sensitive to both: density-viscosity variations within the Earth and lithosphere dynamics. While geoid undulations induced by the mantle dynamics is a subject of numerous studies, the effect of plate tectonics on the geoid and dynamic topography remains an open issue. In present study we investigate a joint effect of weak zones, dividing lithospheric plates, and lateral viscosity variations (LVV) in the whole mantle on the observed geoid. A new numerical technique is based on the substantially revised method introduced by Zhang and Christensen (1993) for solving the Navier-Stokes-Poisson equations in the spectral domain with strong LVV. Weak plate boundaries (WPB) are introduced based on the integrated global model of plate boundary deformations GSRM (Kreemer et al., 2003). We show that the effect of WPB on the geoid is significant and reaches -40 m to 70 m with RMS ~20 m. Maximal WPB-related anomalies are observed over large subduction zones in South America and the Southwestern Pacific in agreement with previous studies. The positive geoid anomaly in South America could be explained largely by a dynamic effect of decoupling of the Nazca and South American plates. Mid-ocean ridges are mostly characterized by negative changes of the geoid compared to the model without WPB. The amplitude of the effect depends on the viscosity contrasts across WPB until its value reaches the limit of 2.5-3 orders of magnitude. This value might be considered as the level at which plates are completely decoupled. The effect of WPB alone, exceeds the effect of LVV in the whole mantle and generally does not correlate with it. However, inclusion of LVV reduces the geoid perturbations due to WPB by about 10 m. Therefore, it is important to consider all these factors together. The geoid changes mainly result from changes of the dynamic topography, which are about -300 to +500 m. The obtained results show that including WPB may significantly improve the reliability of instantaneous global dynamic models. References Zhang, S., and U. Christensen (1993), Some effects of lateral viscosity variations on geoid and surface velocities induced by density anomalies in the mantle, Geophys. J. Int., 114(3), 531-547 Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8-34
Petrunin, Alexey G.; Kaban, Mikhail K.; Schmeling, Harro; Shahraki, Meysam
Owen Fracture Zone: The Arabia-India plate boundary unveiled
NASA Astrophysics Data System (ADS)
We surveyed the Owen Fracture Zone at the boundary between the Arabia and India plates in the NW Indian Ocean using a high-resolution multibeam echo-sounder (Owen cruise, 2009) for search of active faults. Bathymetric data reveal a previously unrecognized submarine fault scarp system running for over 800 km between the Sheba Ridge in the Gulf of Aden and the Makran subduction zone. The primary plate boundary structure is not the bathymetrically high Owen Ridge, but is instead a series of clearly delineated strike-slip fault segments separated by several releasing and restraining bends. Despite an abundant sedimentary supply by the Indus River flowing from the Himalaya, fault scarps are not obscured by recent deposits and can be followed over hundreds of kilometres, pointing to very active tectonics. The total strike-slip displacement of the fault system is 10-12 km, indicating that it has been active for the past ~ 3 to 6 Ma if its current rate of motion of 3 � 1 mm yr - 1 has remained stable. We describe the geometry of this recent fault system, including a major pull-apart basin at the latitude 20�N, and we show that it closely follows an arc of small circle centred on the Arabia-India pole of rotation, as expected for a transform plate boundary.
Fournier, M.; Chamot-Rooke, N.; Rodriguez, M.; Huchon, P.; Petit, C.; Beslier, M. O.; Zaragosi, S.
Sharp Lithosphere-asthenosphere Boundaries of Oceanic Plates
NASA Astrophysics Data System (ADS)
P- and S-receiver function (RF) analysis of borehole broadband ocean bottom seismic data (Kumar et al., 2008, this meeting) and the high-resolution RF image of the subducting Pacific plate beneath the northeast Japan (Kawakatsu, 2008, this meeting) both show the presence of sharp lithosphere-asthenosphere boundaries (LABs) of oceanic plates which appear to show dependence on the plate age. The apparent plate-age dependence of the thickness of the oceanic plate is consistent with a thermally controlled origin for the oceanic LAB, but the fact it is observed in short period (~3s) indicates a sharp boundary (the transition thickness of less than 10-15km), thus a chemical or fabric origin. The observed amplitude of the LAB signals, on the other hand, requires a rather large S-wave speed reduction of ~7%, similar to the observation beneath the eastern North America (Rychert et al., 2007, JGR). One possibility to explain these features is the presence of partial melting in the asthenosphere. The depth of partial melting of the model of Mierdel et al. (2007, Science) estimated using a thermal model incorporating pressure and thermal effect on the thermal diffusivity (Honda&Yuen, 2001, GRL) reproduces the basic trend in the data. For a texturally equilibrated partially molten region, however, a 7% S-wave speed reduction translates into ~3.5% of melting (Takei, 2002, JGR) which may be unrealistically large. The presence of the rather strong LAB signal of oceanic plates reported here may be partly attributed to other mechanisms such as the presence of shear zone of partially-molten region in the asthenosphere (e.g., Holtzman et al., 2003, Science).
Kawakatsu, H.; Kumar, P.; Shinohara, M.; Kanazawa, T.; Araki, E.; Suyehiro, K.
Sediment recycling at convergent plate margins (Indo-Burman Ranges and Andaman-Nicobar Ridge)
NASA Astrophysics Data System (ADS)
Subduction complexes large enough to be exposed subaerially and become significant sources of terrigenous detritus are formed by tectonic accretion above trenches choked with thick sections of remnant-ocean turbidites. They thus need to be connected along strike to a major collision zone, where huge volumes of orogenic detritus are produced and conveyed via a major fluvio-deltaic system to the deep sea. In this article we investigate sediment generation and recycling in the archetype of such settings, the eastern prolongation of the Himalayan collisional system. We illustrate the petrographic and heavy-mineral suites of modern sands produced all along the Indo-Burman-Andaman-Nicobar subduction complex, which includes accreted abyssal-plain sediments overthrust by ophiolites and unconformably overlain by volcaniclastic forearc strata. "Subduction Complex Provenance" is thus composite, and overwhelmingly consists of detritus recycled from largely turbiditic parent rocks (Recycled Clastic Provenance), with local supply from obducted ultramafic and mafic rocks of forearc lithosphere (Ophiolite Provenance) or recycled paleovolcanic to neovolcanic sources (Volcanic Arc Provenance). In order to specifically investigate the effect of recycling, we characterize the diverse detrital signatures of Cenozoic sandstones originally deposited during subsequent stages of "soft" and "hard" Himalayan collision and presently exposed from Bangladesh to the Andaman Islands, and discuss the reasons for compositional discrepancies between parent sandstones and their recycled daughter sands. Long-distance, multistep and multicyclic sediment transfer along and across convergent plate boundaries follows complex trajectories in space and time, which must be resolved whenever we want to obtain a reasonably faithful paleogeographic reconstruction for the recent and less recent geological past.
Garzanti, Eduardo; Limonta, Mara; Resentini, Alberto; Bandopadhyay, Pinaki C.; Najman, Yani; And�, Sergio; Vezzoli, Giovanni
The Plate Boundary Observatory Component of the EarthScope Facility
The Plate Boundary Observatory (PBO), one of the core components of EarthScope, is a geodetic observatory designed to study the three-dimensional strain field resulting from plate boundary deformation in the western US including Alaska. The science goals of PBO require that plate boundary deformation be adequately characterized over the wide range of temporal and spatial scales common to active continental
M. Jackson; W. Prescott
Numerical simulation of shock waves in linear-elastic plates with curvilinear boundaries and material interfaces
An existing numerical scheme of bicharacteristics for linear-elastic, rectangular plates under in-plane impact loading is extended to plates with curvilinear boundaries. In order to validate the employed concept, numerical computations are compared with analytical and experimental results for plates with circular shaped boundaries. Focusing phenomena induced by reflection and refraction at curved outer boundaries and material interfaces are studied.
R. J. Niethammer; K.-S. Kim; J. Ballmann
Buckling transition and boundary layer in non-Euclidean plates.
Non-Euclidean plates are thin elastic bodies having no stress-free configuration, hence exhibiting residual stresses in the absence of external constraints. These bodies are endowed with a three-dimensional reference metric, which may not necessarily be immersible in physical space. Here, based on a recently developed theory for such bodies, we characterize the transition from flat to buckled equilibrium configurations at a critical value of the plate thickness. Depending on the reference metric, the buckling transition may be either continuous or discontinuous. In the infinitely thin plate limit, under the assumption that a limiting configuration exists, we show that the limit is a configuration that minimizes the bending content, among all configurations with zero stretching content (isometric immersions of the midsurface). For small but finite plate thickness, we show the formation of a boundary layer, whose size scales with the square root of the plate thickness and whose shape is determined by a balance between stretching and bending energies. PMID:19658827
Efrati, Efi; Sharon, Eran; Kupferman, Raz
Kinematics of subduction and plate convergence under Taiwan and its geomorphic, geodetic and seismic expressions
NASA Astrophysics Data System (ADS)
Deciphering the kinematics of ongoing subduction and rapid plate convergence under Taiwan is neither trivial nor straightforward. A 3D synthesis of diverse constraints is required, for example tomography, geodesy, tectonic geomorphology, stress inversion, and Philippine Sea plate motions. Eurasian-Philippine Sea plate convergence is ~90mm/y in a mildly oblique 300� azimuth relative to the ~NS nearly vertically subducting Eurasian mantle lithosphere which extends to ~500km depth. If all the current plate convergence were consumed in subduction of Eurasian mantle, the subduction flexural hinge would migrate westward at ~80mm/y, which is fast relative to the ~30mm/y long-term slip rate on the Taiwan main detachment that represents the Eurasian subduction interface under the Taiwan Central Mountains. If this fast simple subduction were occurring, subduction would too quickly outrun the mountain belt in conflict with data. Instead we estimate that subduction of Eurasian lithosphere is proceeding at ~50mm/y with the remaining ~40mm/y convergence at a lithospheric level consumed by secondary subduction above and to the east of the main plate interface. This secondary subduction is largely transient deformation that is most obvious under the Coastal Range, which represents the deforming western margin of the Philippine Sea plate during the last ~1-1.5 Ma. The thrust faults of the Coastal Range function as subduction faults with the long-term net motion of their footwalls moving largely down relative to their only slowly uplifting hanging walls, with a net secondary subduction of ~40-50km in the last ~1-1.5Ma as estimated from seismic tomography and other data. In addition we find evidence for ongoing subduction of the eastern Central Mountains of Taiwan. The crest of the mountains coincides with the western edge of the migrating plate flexure, a band of extensional geodetic strain coincides with the flexure, and an extensional stress state in the upper 5-10km coincides with the zone of flexure. Kinematic modeling of leveling and gps data is consistent with a migration rate of the hinge of ~50mm/y, which would be the subduction rate of Eurasian mantle lithosphere. This rate is somewhat faster than the long-term rate of ~30mm/y since ~15Ma, but less than the current slab-normal plate rate of ~80mm/y, which is thought to represent a speed-up in the last ~1-2Ma. This kinematic modeling also suggests that the main subduction interface under the eastern Central Mountains could be widely locked; if so it has substantial seismic potential at its ~12-13km depth.
Suppe, J.; Carena, S.; Kanda, R. V.; Wu, Y.; Huang, H.; Wu, J. E.
Formation of plate boundaries: The role of mantle volatilization
NASA Astrophysics Data System (ADS)
In the early Earth, convection occurred with the accumulation of thick crust over a weak boundary layer downwelling into the mantle (Davies, G.F., 1992. On the emergence of plate tectonics. Geology 20, 963-966.). This would have transitioned to stagnant-lid convection as the mantle cooled (Solomatov, V.S., Moresi, L.-N., 1997. Three regimes of mantle convection with non-Newtonian viscosity and stagnant lid convection on the terrestrial planets. Geophys. Res. Lett. 24, 1907-1910.) or back to a magma ocean as the mantle heated (Sleep, N., 2000. Evolution of the mode of convection within terrestrial planets. J. Geophys. Res. 105(E7): 17563-17578). Because plate tectonics began operating on the Earth, subduction must have been initiated, thus avoiding these shifts. Based on an analogy with the continental crust subducted beneath Hindu Kush and Burma, we propose that the lithosphere was hydrated and/or carbonated by H2O-CO2 vapors released from magmas generated in upwelling plumes and subsequently volatilized during underthrusting, resulting in lubrication of the thrust above, and subduction of the lithosphere along with the overlying thick crust. Once subduction had been initiated, serpentinized forearc mantle may have formed in a wedge-shaped body above a dehydrating slab. In relict arcs, suture zones, or rifted margins, any agent that warms and dehydrates the wedge would weaken the region surrounding it, and form various types of plate boundaries depending on the operating tectonic stress. Thus, once subduction is initiated, formation of plate boundaries might be facilitated by a major fundamental process: weakening due to the release of pressurized water from the warming serpentinized forearc mantle.
Seno, Tetsuzo; Kirby, Stephen H.
Along-strike Variations of Subduction Parameters at the Chilean Plate Boundary
NASA Astrophysics Data System (ADS)
Newly compiled data of the geometric, kinematic and mechanic properties and their variations along-strike the oblique Chilean subduction margin between 20� S and 46� S are used to weigh their competing influence on forearc deformation. Special emphasis lies on the formation of margin-parallel strike-slip systems. Among the parameters considered are the convergence rate and obliquity, the ocean floor age, the dip of the down-going and the slope of the overriding plate, the geodetic and seismic coupling depth, the interplate seismicity, the depth of the trench-fill and the mass transfer mode at the subduction front. Commonly discussed control factors for forearc deformation can be attributed to three major elements of a subduction system, namely (1) the plate kinematic boundary conditions, (2) the plate coupling properties that govern the effectiveness of force transmission from the subducting plate to the overriding plate, and (3) the upper plate heterogeneities affecting its rheology (e.g. elasticity, shear strength) or resistance to block motion (buttressing). An example is given for each of these elements: (1) Oblique convergence is a pre-requisite for the activation of margin-parallel strike-slip systems, but apparently not a sufficient condition. For example, strike-slip motion can presently be observed along the Liqui�e-Ofqui Fault Zone in southern Chile, while neither the Atacama Fault Zone nor the Precordilleran Fault System in northern Chile accommodate significant amounts of margin-parallel slip since the Pliocene. This difference can not be explained by variations of convergence rate or obliquity as the plate kinematic framework is almost constant along the Chilean trench. (2) The plate coupling force is a function of the frictionally coupled area on the plate interface and of the shear friction that needs to be overcome. Along the Chilean margin various factors affect coupling in opposing manner: The slab-dip is shallower in southern Chile compared to northern Chile, resulting in a greater plate contact area. On the other hand, subduction of younger and hotter oceanic plate in the south could limit the frictionally coupled area (counter acted by increased buoyancy forces?). Subduction of wet sediments in the accretive margin of southern Chile compared to the erosive margin in the north may additionally weaken the interface. (3) The trenchward concave-shaped margin in North-Chile likely hampers margin-parallel motion of a forearc sliver, while strike-slip faulting may be supported in southern Chile due to the lateral proximity of the downdip end of coupling on the plate interface and the rheologically weakened zone of the active volcanic arc. Establishing the current state of plate coupling in southern Chile compared to northern Chile thus remains ambiguous. Margin-parallel strike-slip activity in southern Chile, however, may be facilitated by superposition of two conditions: a shallow-dipping slab that transfers stresses at the base of the overriding plate further arcward and an exceptionally close position of the arc to the trench.
Hoffmann-Rothe, A.; Kukowski, N.; Oncken, O.
Basin boundaries in asymmetric vibrations of a circular plate
NASA Astrophysics Data System (ADS)
In order to investigate further nonlinear asymmetric vibrations of a clamped circular plate under a harmonic excitation, we reexamine a primary resonance, studied by Yeo and Lee [Corrected solvability conditions for non-linear asymmetric vibrations of a circular plate, Journal of Sound and Vibration 257 (2002) 653-665] in which at most three stable steady-state responses (one standing wave and two traveling waves) are observed to exist. Further examination, however, tells that there exist at most five stable steady-state responses: one standing wave and four traveling waves. Two of the traveling waves lose their stability by Hopf bifurcation and have a sequence of period-doubling bifurcations leading to chaos. When the system has five attractors: three equilibrium solutions (one standing wave and two traveling waves) and two chaotic attractors (two modulated traveling waves), the basin boundaries of the attractors on the principal plane are obtained. Also examined is how basin boundaries of the modulated motions (quasi-periodic and chaotic motions) evolve as a system parameter varies. The basin boundaries of the modulated motions turn out to have the fractal nature.
Park, H. D.; Lee, W. K.
An Introduction to Plate Tectonics
NSDL National Science Digital Library
This page is a brief introduction to plate tectonics. It starts with a discussion of the evolution of the theory of plate tectonics and the arguments supporting it. It then discusses the processes associated with tectonics and the types of plate boundaries: divergent, convergent and transform boundaries. It concludes with a discussion of the current hypotheses of what causes plates to move.
Measuring Transient Signals in Plate Boundary Faults Zones with Strainmeters
NASA Astrophysics Data System (ADS)
One of the fundamental goals the U.S. National Science Foundation (NSF) funded Earthscope program was to provide a high-quality, continuous geodetic data set that would allow the scientific community to study the evolution of plate boundary zones. Of particular importance was enabling investigation of the role aseismic transient deformation plays in the release of accumulated stress. For example, to allow the comparison of the amount of strain released through Episodic Tremor and Slip (ETS) events to that released in subduction zone earthquakes or, provide the ability to geodetically illuminate the kinematics of fault creep in strike-slip fault zones. The ability to easily integrate these measurements with compatible geophysical data sets was also an essential objective. With goals such as these in mind NSF funded the Plate Boundary Observatory (PBO) to record the continuous deformation field across the western US Plate Boundary. PBO, built and operated by UNAVCO, now consists of over 1100 GPS stations, 76 co-located borehole strain and seismic sites, 6 long baseline strainmeters, Depending on the scientific questions being addressed sites may also have tiltmeter, meteorological, pore pressure and meteorological instrumentation. This presentation will focus on the transient deformation signals recorded by the PBO strainmeter network. PBO strainmeters, which excel in recording signals on the order of nanostrain over hours, have provided unprecedented temporal resolution of aseismic transients such as ETS events in the Cascadia subduction zone, creep signals along the central section of the San Andreas fault system and tsunami generated strain waves. UNAVCO is responsible not only for the ongoing operation of PBO but also the generation of data products associated with each instrument type. In this presentation we will highlight some of the transient signals these instruments have captured, outline the processing steps required to extract these signals data and describe the strainmeter data products produced by UNAVCO.
Hodgkinson, Kathleen; Mencin, Dave; Phillips, David; Henderson, Brent; Gottlieb, Mike; Gallaher, Warren; Johnson, Wade; Pyatt, Chad; Van Boskirk, Elizabeth; Fox, Otina; Mattioli, Glen; Meertens, Chuck
Diffuse Oceanic Plate Boundaries, Thin Viscous Sheets of Oceanic Lithosphere, and Late Miocene Changes in Plate Motion and Tectonic Regime
Diffuse plate boundaries are often viewed as a characteristic only of continental lithosphere and as a consequence of its rheology, while narrow boundaries and plate rigidity are viewed as characteristic of oceanic lithosphere. Here we review some of the evidence that shows that deformation in the ocean basins is in many places just as diffuse as deformation in the continents.
R. G. Gordon; J. Royer
Convergence of spectral methods for hyperbolic initial-boundary value systems
NASA Technical Reports Server (NTRS)
A convergence proof for spectral approximations is presented for hyperbolic systems with initial and boundary conditions. The Chebyshev collocation is treated in detail, but the final result is readily applicable to other spectral methods, such as Legendre collocation or tau-methods.
Gottlieb, D.; Lustman, L.; Tadmor, E.
Crustal motion along the Eurasia-Nubia plate boundary in the Calabrian Arc and Sicily and active extension in the Messina Straits from GPS measurements
We investigate crustal deformation along the Eurasia-Nubia plate boundary in Calabria and Sicily revealed by the GPS velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns. We recognize two distinct crustal domains characterized by different motions and styles of deformation. Convergence in Sicily is taken up by crustal shortening along the former Tyrrhenian
Nicola D�Agostino; Giulio Selvaggi
A key economic issue is whether poor countries or regions tend to grow faster than rich ones: are there automatic forces that lead to convergence over time in the levels of per capita income and product? We use the neoclassical growth model as a framework to study convergence across the 48 contiguous U.S. states. We exploit data on personal income
Robert J. Barro; Xavier Sala-i-Martin
Significant Variations in the Strength of the Lithosphere-Asthenosphere Boundary Across the California Plate Boundary
NASA Astrophysics Data System (ADS)
To investigate changes in the properties of the lithosphere-asthenosphere transition across a major plate boundary we use Sp common conversion point (CCP) stacked receiver functions to calculate the depth and strength of mantle interfaces beneath a region encompassing most of California, including the boundary between the Pacific and North American Plates, Great Valley, Sierra Nevada, Eastern California Shear Zone and Walker Lane. Using broadband data from permanent stations (including the Southern and Northern California Seismic Networks), the EarthScope Transportable Array, and numerous temporary deployments, we calculated approximately 108,000 individual Sp receiver functions and stacked them in three dimensions using a common conversion point approach. A clear Sp phase consistent with a velocity decrease exists throughout our study region and its depth ranges from 45 to 120 km. The depth of this phase falls within the transition from high velocity lithosphere to slower asthenosphere seen in surface wave tomography and we interpret this phase to be the seismological lithosphere-asthenosphere boundary (LAB). Generally, the depth of the LAB phase varies gradually, with a few exceptions where rapid lateral variations can occur over distances of 25-50 kilometers. For example, in Southern California we observe thinner lithosphere ( ~50 km) beneath the Inner Borderlands, which abruptly transitions to thicker lithosphere beneath the Outer Borderlands (~90 km) and the Western Transverse Range (~85 km), as seen in Lekic et al. (2011). Thinner than average lithosphere (~55 km) is also observed beneath the southern edge of the Great Valley, located in the vicinity of the Isabella Anomaly, and beneath portions of Walker Lane. The most striking feature of the Sp CCP stack is a change in LAB amplitude across the plate boundary. Average phase amplitude beneath crustal blocks translating with motions similar to the Pacific Plate are at least 40% smaller than phase amplitudes for those blocks whose motion more closely aligns with North America. The boundary between the two sets of blocks is often, but not always, co-located with the plate boundary defined by the San Andreas Fault. Where the LAB phase is strong, on the eastern side of the plate boundary, a large and rapid drop in shear velocity is implied, while on the western side of the boundary, the weaker phase indicates a smaller and/or more gradual drop in shear velocity. Comparison to shear-wave splitting and surface wave tomography indicates that the systematic changes in LAB amplitude across the plate boundary are not readily explained by lateral changes in mantle azimuthal anisotropy and surface wave tomography suggests that the variation in LAB amplitude is related to differences in lithospheric mantle velocities (Lin et al. 2011, 2012). In addition, the laterally abrupt nature of the change in LAB amplitude is consistent with an origin in the higher viscosities of the lithosphere. This interpretation implies that some boundaries between crustal blocks observed at the surface persist to the base of the lithosphere.
Ford, H. A.; Fischer, K. M.; Lekic, V.
Seismotectonics and recent evolution of the Eurasia-North America Plate Boundary in Northeastern Russia
NASA Astrophysics Data System (ADS)
In contrast to oceanic plate boundaries which are usually well defined by earthquake locations and magnetic anomalies, the present and past kinematics of plate boundaries in the continents remains problematic in many settings. One particularly vexing such boundary is the one that separates Eurasia from North America in Northeast Russia. In the earliest plate models it was evident that the mid-Atlantic spreading ridge continues in the Arctic as the Gakkel ridge which then runs almost perpendicularly into the continental shelf of Russia in the Laptev sea. On the shelf, and further south on land, the narrow belt of seismicity that is found along the Gakkel ridge broadens into a diffuse swath of earthquakes which is in places more than 800 km wide and extends along the Chersky Range towards the coast of the Okhotsk sea and northern Kamchatka The fact that the Okhotsk sea is aseismic but is surrounded by seismic belts has to lead the interpretation that it is an independent microplate that lies between the Eurasian, North American, Pacific and Amur plates (Cook et al., 1986).Unravelling the kinematics of the Eurasia-Okhotsk-North America Plate boundaries has proven difficult. This is in part due to the paucity of geological and geophysical data from this remote region, and to the fact that the Eurasia-North America pole of rotation lies in close vicinity to the plate boundary itself. Cook et al. (1986), using earthquake slip vectors, placed the current pole of rotation near the Lena river delta, that is, in the area where Eurasia-North America plate boundary comes on shore ). As a consequence, spreading along the Gakkel ridge north of the pole of rotation, should change into convergence or strike-slip to the south depending on the orientation of the boundary. Making specific predictions for fault kinematics in the area has been hampered by the fact that different geophysical and geodetic data-sets have yielded different locations for the Eurasia-North America pole of rotation (Cook et al. 1986; Rowley and Lottes, 1988; De Mets, 1990; Imaev et al., 2000; Kogan et al., 2000). Focal mechanism solutions are predominantly left-lateral and thrust along the Chersky seismic belt, that is, the northern boundary of the Okhotsk plate and right-lateral along its western boundary leading Riegel et al.(1993) to the conclusion that the Okhotsk plate is being extruded to the south. Furthermore, it has been shown on the basis of North Atlantic magnetic and gravity data, that the position of the Eurasia-North America pole of rotation moved significantly over that last 60 my so that the portion of the plate boundary in Northeast Russia changed from predominantly convergent until the Late Cretaceous to divergent until the Early Eocene, followed by various degrees of transpression during the rest of the Cenozoic (Gaina et al., 2002).On the shelf of the Laptev Sea, the Gakkel Ridge gives way to four major continental rift branches with up to 10 km of sedimentary fill spanning from the Late Cretaceous to Recent (Drachev, 1999). Earthquakes are most numerous along the southern margin of the rift system in the Lena delta region and have normal and strike-slip focal mechanism solutions (Imaev et al., 2000). On land, several branches of the rift system overprint the northern termination of the Mesozoic Verkhoyansk fold-and-thrust belt and the accreted arc terranes which are found in its hinterland (Parfenov et al., 1995). Focal mechanism solutions in this area shift from extentional to the north to compressional and strike-slip to the south. The plate boundary continues to the southeast across the Omoloi depression and then follows the trend of major mountain ranges and intermontane basins in the area: the Chersky and Moma ranges and the Moma basin. The Chersky Range, which has the highest topographic elevations in Northeast Russia (3947 m), has a complex history of Mesozoic and Cenozoic deformation (Parfenov and Gaiduk, 2001). The highest peaks are underlain by late Jurassic granite batholiths. Late Oligocene-Miocene deposits along the middle Indigirk
Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. T.; Mackey, K. G.
Features on Venus generated by plate boundary processes
NASA Technical Reports Server (NTRS)
Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.
Mckenzie, Dan; Ford, Peter G.; Johnson, Catherine; Parsons, Barry; Sandwell, David; Saunders, Stephen; Solomon, Sean C.
Tsunami Signals Recorded By Plate Boundary Observatory Borehole Strainmeters
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), the geodetic component of the US National Science Foundation funded Earthscope program, is designed to capture the continuous three-dimensional deformation field across the western United States plate boundary. Installed and maintained by UNAVCO, the observatory currently consists of over 1100 continuous GPS sites, 6 long-baseline laser strainmeters and 75 borehole strainmeters. PBO borehole strainmeters have recorded the arrival of tsunamis generated by the 2009 M8.0 Samoa, 2010 M8.8 Chile and 2011 M9.0 Tohoku earthquakes on the Pacific coast of North America. In our analysis of the strain data we find the following: the tsunami arrival times recorded by the strainmeters are consistent with those recorded by nearby tide-gauges, the data are of sufficient quality to compare the frequency content of the tidal signal in the days before and after the tsunami and, the strain measurements are comparable with those predicted by theory. In each case the strain measurements can be translated to water height estimates which are within centimeters of those recorded by tide gauges. It is possible that borehole strainmeters could play a role in providing a land-based, continuous, high-rate tsunami measurement system.
Hodgkinson, K.; Mencin, D.; Borsa, A.; Henderson, B.; Johnson, W.
Stress accumulation and release at complex transform plate boundaries
Finite element methods are used to model the dynamics of deformation along complex transform plate boundaries, specifically the San Andreas fault system, California. Effects of mantle rheology and fault geometry on the stress buildup and release are investigated. No prior knowledge of the earthquake cycle time or amount of fault slip is assumed that the results suggest that the San Andreas fault slips at low shear stress (about 15 MPa). Although the maximum stress on the fault is 15 MPa, models with an upper mantle shear zone deforming entirely by dislocation creep accumulate stresses that exceed 100 MPa, a stress level high enough to drive localized dynamic recrystallization and a shift in dominant deformation mechanism to diffusion creep. Models in which the mantle shear zone deform locally by diffusion creep reach a dynamic steady state where lithospheric shear stresses never exceed the specified fault stress anywhere in the model and indicate that the strength of the upper mantle is an important parameter in the dynamics of plate boundary deformation. 17 refs.
Verdonck, D.; Furlong, K.P. (Pennsylvania State Univ., University Park (United States))
NSDL National Science Digital Library
This site contains 25 questions on the topic of plate tectonics, which covers the development of the theory, crustal movements, geologic features associated with tectonics, and plate boundaries (convergent, divergent, transform). This is part of the Principles of Earth Science course at the University of South Dakota. Users submit their answers and are provided immediate verification.
Heaton, Timothy
Comparison of Modern Zn-Ba-Pb Ore Deposits at Convergent Plate Margins and Fe-Cu-Zn Deposits at Divergent Plate Margins
At divergent plate margins, black smoke forms immediately on contact of ascending hydrothermal solutions with sea water. The black smoke, consisting mainly of black ore (BO) and barite ore (BaO), is rapidly dispersed in seawater leaving behind a dominantly yellow ore (YO). At convergent plate margins, on the other hand, zinc sulfides and associated chalcophilic elements start depositing within the
G. P. Glasby
Plate boundary processes at the Hadean-Eoarchean transition
NASA Astrophysics Data System (ADS)
The time of the onset of plate interactions on Earth is unknown. Have plate tectonics-like processes been a general feature of Earth since its earliest history? It is important to know this at least when considering planetary heat-loss, element recycling and habitats for the origin of life. We report direct evidence for plate boundary processes before 3.7 Ga from the geochemistry of the oldest supracrustal rocks, which include paragneisses, orthogneisses and mafic schists, from Eoarchean terranes in West Greenland (>3.83 Ga), northern Quebec (>3.75 Ga) and in a Hadean rock from northwestern Canada (ca. 4.03 Ga). Compositions for these lithologies strongly resemble the products of contemporary arc and back-arc plutonic and volcanosedimentary systems. Metamorphic equivalents of tonalite-trondhjemite suites captured in the oldest terranes show that continental precursors were widespread on Earth since at least ca. 3.83 Ga. Yet earlier geochemical indicators from oxygen- and hafnium isotopes, and mineral inclusions in Hadean detrital zircons (3.83 - 4.38 Ga), reinforce the view that subduction-like settings where partial melting of a subduction slab (or thickened mafic lower crust?) have operated on Earth since ~150 Myr after the formation of the Moon. Apparently, heterogeneities induced by earlier Hadean crust-forming events were almost entirely lost by vigorous early mantle mixing by the time of formation of the oldest known rocks.
Cates, N. L.; Mojzsis, S. J.
New GPS constraints on active deformation along the Africa-Iberia plate boundary
NASA Astrophysics Data System (ADS)
We use velocities from 65 continuous stations and 31 survey-mode GPS sites as well as kinematic modeling to investigate present day deformation along the Africa-Iberia plate boundary zone in the western Mediterranean region. The GPS velocity field shows southwestward motion of the central part of the Rif Mountains in northern Morocco with respect to Africa varying between 3.5 and 4.0 mm/yr, consistent with prior published results. Stations in the southwestern part of the Betic Mountains of southern Spain move west-southwest with respect to Eurasia (� 2-3 mm/yr). The western component of Betics motion is consistent with partial transfer of Nubia-Eurasia plate motion into the southern Betics. The southward component of Betics motion with respect to Iberia is kinematically consistent with south to southwest motion of the Rif Mountains with respect to Africa. We use block modeling, constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures. Our preferred plate boundary geometry includes one block between Iberia and Africa including the SW Betics, Alboran Sea, and central Rif. This geometry provides a good fit to the observed motions, suggesting a wide transpressive boundary in the westernmost Mediterranean, with deformation mainly accommodated by the Gloria-Azores fault system to the West and the Rif-Tell lineament to the East. Block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles: (i) extension along the NE-SW trending Trans-Alboran shear zone, (ii) dextral strike-slip in the Betics corresponding to a well defined E-W seismic lineament, and (iii) right lateral strike-slip motion extending West to the Azores and right-lateral motion with compression extending East along the Algerian Tell. We interpret differential motion in the Rif-Alboran-Betic system to be driven both by surface processes related the Africa-Eurasia oblique convergence and sub-crustal dynamic processes associated with the long history of subduction of the Neotethys ocean lithosphere. The dextral slip identified in the Betic Mountains in Southern Spain may be related to the offshore fault that produced the Great 1755 Lisbon Earthquake, and as such may represent a significant seismic hazard for the West Mediterranean region.
Koulali, A.; Ouazar, D.; Tahayt, A.; King, R. W.; Vernant, P.; Reilinger, R. E.; McClusky, S.; Mourabit, T.; Davila, J. M.; Amraoui, N.
Structural Setting and Post-miocene Evolution of The Antarctic/pacific Plate Boundary Close To The Macquarie Triple Junction.
NASA Astrophysics Data System (ADS)
The southern sector of the SW Pacific Ocean, south of 60S, is one of the less inves- tigated areas of our planet, although is a key point for studying the kinematics and the tectonic interactions of three major plates, Antarctic, Pacific and Australian, as they meet at the Macquarie Triple Junction (MTJ). Satellite-derived images of the ocean floor constitute the only morphostructural data-set available to date for this remote re- gion. Free-air gravity anomaly, as well as predicted-topography maps, outline a great complexity, and an overall geometrical and structural variability. The Pacific-Antarctic boundary SE of the MTJ is formed by a sequence of short ridge axes, dissected by a set of close-spaced fracture zones. This configuration is probably related to a recent (late Miocene) plate reorganization, that caused transtension across an abandoned trans- form/transcurrent boundary, and the formation of a "leaky transform system", which subsequently developed in well organized, equally-spaced ridge/transform segments. A focused re-processing of multichannel seismic reflection profiles acquired in this area during the early '90, in conjunction with more recent geomagnetic data, allow us to depict the post-Miocene evolution of this sector of the Antarctic/Pacific plate boundary. Data analysis led to the conclusion that two major deformation processes have contributed to shape the plate boundary in this region, convergence and strike-slip tectonics. They were probably active during different phases and/or in combination. Although teleseismic data show that the present-day boundary is dominated by exten- sional deformations, evidence of compressions are observed SE of the MTJ, along the westernmost Pacific-Antarctic margin. This suggests an unexpected structural conti- nuity between the present-day Pacific/Australian margin north of the MTJ (the Hjort Trench and the southern part of the Macquarie Ridge Complex), and a wide sector of the Pacific plate along the Pacific/Antarctic boundary.
Gasperini, L.; Fabretti, P.; Lodolo, E.
The Plate Boundary Observatory: Community Focused Web Services
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of channels, including map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.
Matykiewicz, J.; Anderson, G.; Lee, E.; Hoyt, B.; Hodgkinson, K.; Persson, E.; Wright, J.; Torrez, D.; Jackson, M.
Patterns of seismogenesis for giant plate-boundary earthquakes in island-arc-type subduction systems
NASA Astrophysics Data System (ADS)
The global record of giant earthquake occurrence in subduction zones during the instrumental and historical eras is woefully short; only about 16 events with magnitudes above 8.4 are reasonably well documented since 1700. We find no examples of giant (M > 8.4) interplate thrust events and/or wide-ranging tsunamis sourced in the classic island arcs with fast backarc spreading (Bonin, Marianas, Tonga-Kermadec, Vanuatu, and South Scotia). The Sumatra-Andaman Earthquake of 2004 (SAE) ruptured a sector of the INDIA-BURMA subduction boundary and evidently had no known historical antecedents, suggesting that the return time may be many centuries to millennia and consistent with low convergence rates. Moreover, the persistence of rupture to the north in the weakly volcanic Nicobar/Andaman sector gives one pause to reflect on the assumption that island arcs, especially those with active back-arc spreading such as the Marianas, do not produce great interplate- thrust earthquakes. The Andaman/Nicobar subduction segment is an unusual island arc. Only two arc volcanoes occur between the convergent plate boundary west of the Andamans and the backarc ridge/transform system to the east. Backarc spreading in the Andaman/ Nicobar segment is unusual because the NNW spreading directions are nearly parallel to the trench/deformation-front as do the INDIA-BURMA plate motions across it. This geometry suggests that arc-normal extension, trench migration and associated slab normal motions may not mechanically decouple this subduction system. The Nicobar sector of the rupture for the 2004 event is roughly 200 km wide judging from the aftershock distribution; a distribution that persists to the east under the Nicobar Islands, suggesting that the plate-boundary dip is very shallow in that latitude range. If this is correct, then the down-dip limitation on seismogenic slip set by serpentinized forearc mantle (Hyndman et al., 2003) may not control rupture width as it apparently does for many island arcs with steeper slab dips. Finally, this subduction system receives a large sediment influx from the giant Irrawadi and Ganges River delta systems to the north that drain the active collisional mountain belts further north. High sediment influx and trench sediment acumulation are factors that are present in 12 of the 14 subduction zones that have hosted the giant interplate thrust earthquakes mentioned earlier. This influx appears to be important in the development of a subduction channel of granular material in the plate boundary that may enable ruptures to run to great lengths by smoothing out barriers to earthquake slip. Several island-arc subduction systems (the Manus, SW Ryukyu, W Aleutians, and possibly the South Shetlands systems) have attributes similar to the Nicobar/Andaman segment of the SAE rupture. Moreover, arc volcanic activity is weak or absent and convergence also tends to be slow in all of these island-arc systems. Research done in collaboration with the USGS Tsunami Source Working Group (Steve Kirby and Eric Geist (Co-Chairs) David Scholl, Roland von Huene, Rick Blakely, Ray Wells, and Willie Lee (Secretary))
Kirby, S. H.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to: Architecture, design and performance of optical wide-area-network (WAN), metro, and access networks Integration strategies for multiservice transport platforms Access methods that bridge traditional and emerging services Network signaling and control methodologies All-optical packet routing and switching techniques
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to: Architecture, design and performance of optical wide-area-network (WAN), metro, and access networks Integration strategies for multiservice transport platforms Access methods that bridge traditional and emerging services Network signaling and control methodologies All-optical packet routing and switching techniques
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to: Architecture, design and performance of optical wide-area-network (WAN), metro, and access networks Integration strategies for multiservice transport platforms Access methods that bridge traditional and emerging services Network signaling and control methodologies All-optical packet routing and switching techniques
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to: Architecture, design and performance of optical wide-area-network (WAN), metro, and access networks Integration strategies for multiservice transport platforms Access methods that bridge traditional and emerging services Network signaling and control methodologies All-optical packet routing and switching techniques
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
NASA Astrophysics Data System (ADS)
Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:
Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.
Crustal Deformation at the Arabian Plate-Boundary observed by InSAR
NASA Astrophysics Data System (ADS)
The Arabian plate is bounded by a variety of active plate boundaries, with extension in the Red Sea and Gulf of Aden to the south, compression in Turkey and Iran to the north, and transform faults to the west and to the east. Internally, however, the Arabian plate has been shown to be tectonically rather stable, despite evidence of recent volcanism and earthquake faulting. We use InSAR observations to study recent tectonic and volcanic activity at several locations at the Arabian plate boundary as well within the plate itself. The region near the triple junction between the Arabian, Eurasian, and Anatolian plates has often been the focus of studies on continental deformation behavior and interseismic deformation. Here we use large-scale InSAR data processing to map the deformation near the triple junction and find the deformation to be focused on major faults with little intra-plate deformation. The eastern part of the East Anatolian Fault appears to have a very shallow locking depth with limited fault-normal deformation. Several major earthquakes that have occurred in recent years on the Arabian plate boundary, including the 2011 magnitude 7.1 Van earthquake in eastern Turkey. It occurred as a result of convergence of the Arabian plate towards Eurasia and caused significant surface deformation that we have analyzed with multiple coseismic InSAR, GPS, and coastal uplift observations. We use high-resolution Cosmo-Skymed and TerraSAR-X data to derive 3D coseismic displacements from offsets alone, as some of the interferograms are almost completely incoherent. By identifying point-like targets within the images, we were able to derive accurate pixel offsets between SAR sub-images containing such targets, which we used to estimate the 3D coseismic displacements. The derived 3D displacement field helped in constraining the causative northward dipping thrust-fault. The Qadimah fault is a recently discovered fault located on the Red Sea coast north of Jeddah and under the King Abdullah Economic City, a planned $50 billion harbor city. The fault is a normal fault, parallel to the Red Sea, but it is unclear if the fault is still active and poses significant hazard to the new city. We use MERIS-corrected Envisat InSAR data to study the limited interseismic deformation across the fault and the results suggest that more investigations will be needed to assess the activity of the fault. Several volcanic events have taken place in the region during the past several years, including the 2007-8 Jebel at Tair island (Red Sea) eruption, the 2009 Harrat Lunayyir (western Saudi Arabia) magmatic intrusion, and the 2011-12 Zubair islands (Red Sea) eruption. All these three volcanic events were fed by dike intrusions whose geometry we constrain using the InSAR and optical data. The derived dike orientations provide information about extensional stress field in and around the Red Sea, although on Tair island the upper-most part of the feeder dike was controlled by local stresses within the volcanic edifice.
Jonsson, S.; Cavali�, O.; Akoglu, A. M.; Wang, T.; Xu, W.; Feng, G.; Dutta, R.; Abdullin, A. K.
Sediment subduction - A probable key for seismicity and tectonics at active plate boundaries
A model involving extensive occurrence of sediment subduction and viscous interaction of lithospheric plates at convergent zones is applied to derive simple relations between extremal values of seismic and global tectonic parameters. The strength of mechanical coupling at the interface zone is defined as the maximum shear stress at the base of the over-thrusting plate. A test of these relations
Vladimir Kostoglodov
Obliquely convergent plate motion and its relation with forearc sliver movement, El Salvador volcanic arc
NASA Astrophysics Data System (ADS)
The magmatic arc in El Salvador is interpreted to result from the subduction of the Cocos plate underneath the Caribbean plate along the Middle America trench. In addition, El Salvador contains a fore-arc sliver that moves 11 mm/yr westward relative to the back-arc. Well-defined strike-slip faults along the magmatic arc accommodate forearc sliver motion, but are offset at several locations by en echelon pull-apart step-overs with abundant normal faults. All basaltic-andesitic magmatic centers (San Miguel, San Vincente, San Salvador, Santa Ana) are located within these step-overs, while the two major rhyolitic calderas (Ilopango, Coatepeque) occur directly along the strike-slip faults. There are two puzzling aspects about the strike-slip tectonism. First, a silicic, shallow magma body that intrudes the San Miguel fault zone (part of the El Salvador fault system) was emplaced syn-tectonically (sigmoidal field and magnetic foliations, subhorizontally plunging magnetic lineations and dextral shear at the microscale). Within the dextrally sheared portion of the intrusion, an obsidian band with a 40Ar/39Ar age of 7.46 Ma indicates that dextral strike-slip tectonism in the Salvadoran arc has been an ongoing process for ~7.5 Ma. This casts significant doubt on whether Cocos ridge subduction (that started ~1 Ma ago) is the cause of the ongoing forearc movement. The potentially more significant problem is that the fore-arc sliver in El Salvador moves 11 mm/yr westward relative to the back-arc despite a nearly orthogonal angle of convergence (with a convergence rate of ~77 mm/yr) near El Salvador and absence of significant frictional coupling along the subduction interface. Further, GPS indicates that the Nicaraguan and Salvadoran forearcs define a semi-rigid sliver moving at nearly the same trench-parallel rates despite along-trench changes in the subduction angle. Consequently, it is tempting to attribute the movement of both forearc slivers to Cocos ridge subduction. However, as mentioned above, initiation of strike-slip movement during collision of the Cocos ridge appears incompatible with Miocene strike-slip deformation that occurs. These examples serve to highlight the difficulties in understanding forearc movement in obliquely convergent systems, even in relatively modern belts where the plate motions are well constrained.
Tikoff, B.; DeMets, C.; Garibaldi, N.; Hernandez, W.; Hernandez, D.
The Plate Boundary Observatory: Data Management Progress and Highlights
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 891 continuous GPS stations, up to 174 borehole strainmeter stations, and five laser strainmeters, over the next five years. In addition, 209 previously existing continuous GPS stations will be incorporated into PBO through the PBO Nucleus project, and there will be a pool of 100 portable GPS receivers available for survey-mode observations. To date, 209 PBO GPS stations have been installed, of which 182 have returned data. In addition, PBO now handles data flow for 29 PBO Nucleus stations. Most of these stations return data to the PBO data center in Boulder on a daily basis. These data are then processed by the PBO GPS Analysis Centers, at Central Washington University and the University of California, Berkeley, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. At present, these centers are processing data on a daily basis from about 300 stations; typical position uncertainties are approximately 1.5 mm horizontally and 4 mm vertically, both of which will improve as more data are analyzed. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive under development at the IRIS Data Management Center. PBO now has six borehole strainmeters and one laser strainmeter installed, with data returned at least once per day, and PBO handles data flow for a previously installed laser strainmeter as well. These data are analyzed on a daily basis by the Borehole Strainmeter Data Analysis Center in Socorro, New Mexico, and the Laser Strainmeter Data Analysis Center at the University of California, San Diego. These groups transform the raw strainmeter observations into cleaned individual strain gauge components; time series of shear, areal, and linear strain; and related products. All strainmeter data products are archived at and available from the Northern California Earthquake Data Center and the IRIS DMC.
Anderson, G.; Hodgkinson, K.; Jackson, M.; Wright, J.
Logistical Support for the Installation of the Plate Boundary Observatory GPS and Borehole Strainmeter Networks
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser
C. Kurnik; K. Austin; B. Coyle; T. Dittmann; K. Feaux; B. Friesen; W. Johnson; D. Mencin; B. Pauk; C. Walls
EarthScope Plate Boundary Observatory Data in the College Classroom (Invited)
The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3-D strain field across the active boundary zone between the Pacific and North American tectonics plates in the western United States. All PBO data are freely available to scientific and educational communities and have been incorporated into a variety of activities for college
S. C. Eriksson; S. E. Olds
Tidal calibration of plate boundary observatory borehole strainmeters
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory, the geodetic component of the EarthScope program, includes 74 borehole strainmeters installed in the western United States and on Vancouver Island, Canada. In this study, we calibrate 45 of the instruments by comparing the observed M2 and O1 Earth tides with those predicted using Earth tide models. For each strainmeter, we invert for a coupling matrix that relates the gauge measurements to the regional strain field assuming only that the measured strains are linear combinations of the regional areal and shear strains. We compare these matrices to those found when constraints are imposed which require the coupling coefficients to lie within expected ranges for this strainmeter design. Similar unconstrained and constrained coupling matrices suggest the instrument is functioning as expected as no other coupling matrix can be found that better reduces the misfit between observed and predicted tides when the inversion is unconstrained. Differences imply a coupling matrix with coefficients outside typical ranges gives a better fit between the observed and predicted tides. We find that 22 of the strainmeters examined have coupling matrices for which there is little difference between the constrained and unconstrained inversions. If we allow a greater divergence in the shear coupling coefficients and consider the possibility that one gauge may not function as expected, the discrepancies between the unconstrained and constrained coupling matrices are resolved for a subset of the remaining strainmeters. Our results also indicate that most of the strainmeters are less sensitive to areal strain than expected from theory.
Hodgkinson, Kathleen; Langbein, John; Henderson, Brent; Mencin, Dave; Borsa, Adrian
NSDL National Science Digital Library
Some math teachers find themselves confronted by students who ask, "Why do we have to learn this?" or "When am I going to use it?" These are vexing questions for sure, and one suggestion might be to incorporate the history and development of the field of mathematics into the formal study of the subject. That is exactly what a dedicated team of individuals at the Mathematical Association of America (MAA) and the National Council of Teachers of Mathematics decided to do when they created the online magazine, Convergence. The magazine contains a wide range of materials for educators, including animated mathematical demonstrations that can be downloaded for classroom use and discussions of particular problems from an historical context. On the magazine's homepage, visitors can view featured articles, take a look over the "Critic's Corner", and use the "Show Me" search engine to look for new and compelling additions.
The Plate Boundary Observatory: Data Management Progress and Highlights
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations through the PBO Nucleus project. As of 1 September 2006, the PBO GPS network was halfway completed with 426 stations installed, of which 400 have returned data, and PBO handled data flow for 120 PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with 16 returning data on an hourly basis. Overall, the combined PBO and Nucleus networks had returned almost 150 GB of raw GPS data as of September 2006. These data are then processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2006, these centers processed data on a daily basis from about 590 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/?pageid=88. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2006, 19 PBO borehole stations had been installed and two laser strainmeter stations were operating, with a total of 28 borehole stations and 3 laser strainmeters expected by the end of 2006. Seismic data flow in real time to the Boulder NOC for initial quality checks, and thence to the IRIS DMC for final quality checks, archiving, and distribution; all PBO seismic data flow is via the Antelope software suite. Strainmeter data flow hourly and daily to the Boulder NOC and thence to the Borehole Strainmeter Analysis Center in Socorro, New Mexico, and the Laser Strainmeter Analysis Center at the University of California, San Diego. These groups transform the raw strainmeter observations into cleaned individual strain gauge components; time series of shear, areal, and linear strain; and related products. All strainmeter data products are archived at and available from the Northern California Earthquake Data Center and the IRIS DMC, in both the native raw formats and SEED format; all seismic data products are archived at and available from the IRIS DMC, in SEED format. By September 2006, the PBO seismic network had provided 60 GB of raw data, and the PBO strainmeter network had provided 27.5 GB of raw data. Please visit http://pboweb.unavco.org/?pageid=89 for more information on data products from the PBO strainmeter and seismic networks.
Anderson, G.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Wright, J.; Jackson, M.; Prescott, W.
An EarthScope Plate Boundary Observatory Progress Report
NASA Astrophysics Data System (ADS)
UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest in the world. Data from the PBO network will facilitate research into plate boundary deformation with unprecedented scope and detail. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Highlights of the past year's work include the expansion of the Alaska subnetwork to 95 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and has expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating, with a total of 60 borehole stations and 4 laser strainmeters expected by October 2007. In response to direction from the EarthScope community, UNAVCO installed a dense network of six stations along the San Jacinto Fault near Anza, California; installed three of four planned borehole strainmeter stations on Mt. St. Helens; and has densified coverage of the Parkfield area. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network provides 350 GB of raw standard rate data, with special downloads of more than 250 GB of high-rate GPS data following large earthquakes in Russia, Tonga, and Peru, as well as for community requests. The standard rate GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 201 GB of raw data, which are available via Antelope and Earthworm from PBO and via the IRIS Data Management Center (DMC); we provide data to seismic networks operated from Caltech, UCSD, UCSB, University of Washington, and the Pacific Geosciences Center in Sidney, BC. The PBO strainmeter network has provided 93 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/gps_data and http://pboweb.unavco.org/strain_data for more information on PBO GPS and strainmeter/seismic data products, respectively.
Jackson, M.; Anderson, G.; Blume, F.; Walls, C.; Coyle, B.; Feaux, K.; Friesen, B.; Phillips, D.; Hafner, K.; Johnson, W.; Mencin, D.; Pauk, B.; Dittmann, T.
The Plate Boundary Observatory: Data Management Progress and Highlights
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008, as well as manage data for 209 previously existing continuous GPS stations and one laser strainmeter through the PBO Nucleus project and 11 GPS stations installed by the USArray segment of EarthScope. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with about 40 stations returning data on an hourly basis. Overall, the combined PBO and Nucleus network has now provided almost 350 GB of raw standard rate data, which are routinely processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2007, these centers processed data on a daily basis from about 920 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/gps_data. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating. Seismic data flow in real time to the Boulder NOC for initial quality checks, and then to the IRIS DMC for final quality checks, archiving, and distribution; all PBO seismic data flow is via the Antelope software suite. Strainmeter data flow hourly and daily to the Boulder NOC and then to the Borehole Strainmeter Analysis Center in Socorro, New Mexico, and the Laser Strainmeter Analysis Center at the University of California, San Diego. These groups transform the raw strainmeter observations into cleaned individual strain gauge components; time series of shear, areal, and linear strain; and related products. All strainmeter data products are archived at and available from the Northern California Earthquake Data Center and the IRIS DMC, in both the native raw formats and SEED format; all seismic data products are archived at and available from the IRIS DMC, in SEED format. By September 2007, the PBO seismic network had provided more than 200 GB of raw data, and the PBO strainmeter network had provided almost 100 GB of raw data. Please visit http://pboweb.unavco.org/strain_data for more information on data products from the PBO strainmeter and seismic networks.
Anderson, G.; Blackman, B.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Henderson, B.; Hoyt, B.; Lee, E.; Persson, E.; Smith, J.; Torrez, D.; Wright, J.; Jackson, M.; Meertens, C.
Isla del Coco, on Cocos Plate, Converges with Isla de San Andr�s, on the Caribbean Plate, at 78 mm/yr
NASA Astrophysics Data System (ADS)
Isla del Coco is the only land mass of the Cocos Plate that emerges above sea level. This makes it the only place where Cocos Plate motion can be measured using Global Navigation Satellite System (GNSS) monitoring. Global Positioning System (GPS) observations have been carried out sporadically over more than two decades on Isla del Coco, allowing precise measurement of the motion of the Cocos Plate. Recently, in May 2011, a continuous GPS station was built and instrumented at Isla del Coco, in Wafer Bay, by OVSICORI UNA and UNAVCO, as part of the COCONet regional GNSS network. Position time series from this CGPS station (ISCO: Isla del Coco) show a steady motion of Isla del Coco at a speed of 90.9�1.5mm/yr in the N35oE direction in ITRF2008 and convergence with the Caribbean Plate at 78�1mm/yr. This result is consistent with the findings of the earliest GPS studies, and agrees within uncertainty with the estimated convergence rate of 76.4�2.6 mm/yr of the MORVEL plate motion model. MORVEL is based on an average over the last 780,000 years, and our result suggests that Cocos Caribbean plate motions have been constant over that time interval.
Protti, M.; Gonzalez, V. M.; Freymueller, J. T.; Doelger, S.
Overview on the Plate Boundaries Along the Western Mexican Pacific Margin
NASA Astrophysics Data System (ADS)
The cinematic of the Pacific, Rivera and Cocos oceanic plates have a significant impact on the subduction process and seismic cycles occurring along the western Mexican Pacific margin of the North American and Caribbean plates. Sections of Pacific (PAC), Rivera (RIV), Cocos (COC), North American (NAM) and Caribbean (CAB) plate boundaries along the western margin of Mexico are not well constrained. From north to south: the transform-rift system at Gulf of California has been generally considered as part of PAC-NAM plate boundary. However results of the FAMEX cruise at 2002 evidenced that Tosco-Abreojos Fault System along the western margin of Baja California Peninsula is active. Should this tectonic structure be considered as a plate boundary? At the RIV plate northern corner (including Mazatlan Basin), the scatter seismicity recorded between Tamayo FZ and the Marias Islands restricts the characterization of the plate boundary between the RIV and NAM plates. Some authors have proposed that Tamayo FZ and Marias I. Escarpment are the RIV-NAM plate boundary. Recently other authors have called that RIV-NAM boundary is a geomorphology lineament that runs from a Rivera Rise transform at 23N to the northern end of Marias I. Escarpment. Even so this concept is not sustained with seismic activity. Further this thought would imply that the oceanic lithosphere of Mazatlan Basin would form part of NAM plate. Other thoughts are either that there is a diffuse RIV-NAM plate boundary to the north of the Maria Archipelago, or Middle America Subduction Zone is gradually extending northward of the Maria Is. While the plate boundary at SE corner of the RIV plate is neither well defined morphologically nor seismically constraint, offshore Colima Coast. Some authors have proposed that this zone is a diffuse plate boundary between RIV and COC plates, result of a NE-SW shear plate motion. Other authors have proposed that the RIV-COC boundary extends E-W from the El Gordo Graben (EGG) at the Middle American Trench (MAT) to northern tip of the East Pacific Rise (EPR). Results of recently multibeam and magnetic surveys indicate that this boundary is possible segmented as an echelon E-W structure, north of EGG. Clearly these hypotheses on the RIV-COC plate boundary show that its configuration is neither well seismic nor morphology constrained. To the south, the triple junction point of COC, NAM, and CAB plate boundaries is also another case where the boundaries are poorly constrained seismically and morphologically. Traditionally, the COC-NAM-CAB triple junction point has been positioned where the MAT trend bends by the Tehuantepec Ridge (TR) collision, but no offshore geophysical data sustain that NAM-CAB plate boundary extends to MAT-TR point. In the last decade, the Servicio Sismol�gico Nacional (SSN) has extended its seismic station network at the southern Mexican territory. From this data, the distribution of offshore earthquakes covers a broad marine zone in front the Chiapas and Guatemala coastline and does not show a defined earthquake concentration associated to the proposed offshore extension of the Polochic-Motogua Fault through Guatemala and Mapastepec Fault through Chiapas, Mexico.
Mortera-Gutierrez, C. A.; Bandy, W. L.; Michaud, F.; Ortega Ram�rez, J.
Experimental validation of the sound transmission of rectangular baffled plates with general elastic boundary conditions.
Several prediction methods have recently been developed for systematically studying the effects of general boundary conditions on the sound transmission loss (STL) of plate-like structures. But corresponding experimental validation studies remain scarce owing to the difficulty of obtaining accurate boundary conditions for practical structures. This paper presents a convincing experiment conducted on a baffled plate system to validate the STL prediction model in a previous paper by Yu et al. [Noise Control Eng. J. 58(2), 187-200, 2010]. A method is proposed to determine the boundary conditions of this system, and experimental STL compares well with the predictions based on the identified boundary condition. PMID:21682364
Ou, Dayi; Mak, Cheuk Ming
From transtension to transpression along the northern Caribbean plate boundary off Cuba: implications for the Recent motion of the Caribbean plate
NASA Astrophysics Data System (ADS)
Marine geophysical surveys using Seabeam, single-channel seismic reflection, gravimetric and magnetic measurements have been conducted along a segment of the northern Caribbean transcurrent plate boundary (SEACARIB II cruise). The data allow a better definition of the geometry and the tectonic regime of this major strike-slip area. They support the following results: (1) Along the southern Cuban margin, the Oriente fault displays a discontinuous trace, mainly composed of dextral offset, "en echelon" segments. Some pull-apart basins are located between fault segments (Cabo Cruz basin, Chivirico and Baitiquiri basins). In the Windward Passage area, the plate boundary enters into the Tortue Channel and is not connected with the subduction front off northern Hispaniola. (2) The eastern part of the Oriente Deep and the Santiago Promontory are characterised by active compressional tectonics. They form the Santiago Deformed Belt, described here for the first time. This deformed belt can be divided longitudinally into three main segments, each one characterised by a particular tectonic style. Its development is related to a transpressional mechanism along the left-lateral Oriente strike-slip fault. Our observations suggest that a tectonic and kinematic reorganisation occurred recently in this area, probably in the Late Pliocene, which may be compared with the recent geological events recorded on land in the northern Caribbean domain. The precise knowledge of both geometry and structures along the Oriente strike-slip fault south of Cuba provides new constraints for the recent kinematic evolution along the northern Caribbean transcurrent plate boundary: it leads us to infer the existence of a convergence component associated with the slip component along the Oriente transform fault.
Calais, Eric; de Lepinay, Bernard Mercier
NSDL National Science Digital Library
This interactive site uses illustrations and photographs along with text to explain the movement of tectonic plates and the result of this movement on the surface of the Earth. There is a detailed discussion of the movement at each of the four types of plate boundaries: divergent, convergent, transform, and plate boundary zones. Both lateral and vertical movements are depicted by maps and diagrams and resulting Earth structures are shown in photographs.
Dynamic characteristics analysis of active constrained layer damping plate with various boundary conditions
NASA Astrophysics Data System (ADS)
Considering the direct and converse piezoelectric effect, expressions of piezoelectric membrane internal forces in the piezoelectric constrained layer were given. The control equations of the piezoelectric constrained layer and host plate were obtained in according with the thin plate theory. Based on the layer wised principle, the integrated first order differential equation of an active constrained layer damping (ACLD) plate was derived for the simply supported boundary condition. Then, this method was expanded to the ACLD plate with cantilever boundary condition by virtue of geometric analogy method. Employing the extended homogeneous capacity precision integration approach, a high precision semi-analytical method was proposed to analyze the dynamic characteristics of the ACLD plate with various boundary conditions. The comparison with the literature results has verified the accuracy and effectiveness of the present method.
Lu, Jing; Xiang, Yu; Ni, Qiao
Recovering physical property information from subduction plate boundaries using 3D full-waveform seismic inversion
NASA Astrophysics Data System (ADS)
Our understanding of subduction margin seismogenesis has been revolutionised in the last couple of decades with the discovery that the size of the seismogenic zone may not be controlled simply by temperature and a broad spectrum of seismic behaviour exists from stick-slip to stable sliding. Laboratory and numerical experiments suggest that physical properties, particularly fluid pressure may play an important role in controlling the seismic behaviour of subduction margins. Although drilling can provide information on physical properties along subduction thrust faults at point locations at relatively shallow depths, correlations between physical properties and seismic velocity using rock physics relationships are required to resolve physical properties along the margin and down-dip. Therefore, high resolution seismic velocity models are key to recovering physical property information at subduction plate boundaries away from drill sites. 3D Full waveform inversion (FWI) is a technique pioneered by the oil industry to obtain high-resolution high-fidelity models of physical properties in the sub-surface. 3D FWI involves the inversion of low-frequency (>2 to <7 Hz), early arriving (principally transmitted) seismic data, to recover the macro (intermediate to long-wavelength) velocity structure. Although 2D FWI has been used to improve velocity models of subduction plate boundaries before, 3D FWI has not yet been attempted. 3D inversions have superior convergence and accuracy, as they sample the subsurface with multi-azimuth multiply-crossing wavefields. In this contribution we perform a suite of synthetic tests to investigate if 3D FWI could be used to better resolve physical property information along subduction margin plate boundaries using conventionally collected 3D seismic data. We base our analysis on the Muroto Basin area of the Nankai margin and investigate if the acquisition parameters and geometry of the subduction margin render 3D seismic data collected across this basin in 1999 suitable for future 3D FWI. We build a 3D model of the sub-surface based on an existing velocity model that was used to migrate these data (Tsuji et al. 2000, JGR). We then add a low P-wave velocity layer along the d�collement, which is supported by ODP core data but does not feature in the current seismic velocity model, to test if it could be recovered using 3D FWI. We use the same acquisition parameters as in the 1999 seismic survey (including a 6 km long streamer) to generate a fully-elastic synthetic seismic dataset, added noise and inverted the windowed transmitted arrivals only. We also ran a suite of resolution tests across the model. The results show that 3D FWI of conventionally collected 3D seismic data across the Muroto Basin would be capable of resolving variations in P-wave velocity along the d�collement of the order of half the seismic wavelength at the plate boundary. This is a significant improvement on conventional travel-time tomography which resolves to the Fresnel width. In this presentation we will also postulate on the optimal 3D FWI experiment design for the next generation of 3D seismic surveys across subduction margins as a guide for those embarking on new data collection.
Bell, R. E.; Morgan, J. V.; Warner, M.
Spatial and Temporal Variations Along the New Zealand Plate Boundary: Decoupling, Delamination, and Localization
NASA Astrophysics Data System (ADS)
New Zealand sits astride the Pacific-Australia plate boundary and hosts two fundamental transitions in plate interactions. Subduction of the Pacific plate beneath the North Island along the Hikurangi margin ends and the plate motion is taken up along the Alpine Fault translational plate boundary in the Marlborough-Kaikoura regions of the South Island. This subduction-translation transition has migrated southward since 20-25 Ma. In the south, a small sliver of the Australia plate subducts beneath the Fiordland region, accommodating an � 100 km transpressional left-step in the Australia-Pacific plate boundary south of the South Island. At the northern termination of this small subduction zone the Alpine Fault initiates. This subduction-translation-subduction plate boundary structure has undergone significant evolution over the past 15-20 million years, driven by changes in relative plate motion and significant lithospheric deformation focused in the transition zones along the plate boundary. At the northern transition, we argue that the encroaching subducted Pacific slab acts as a chisel on the lower lithosphere of the overriding Australian plate driving the active delamination of much of the mantle lithosphere. This mass removal makes the necessary space to accommodate the slab. Additionally it drives substantial vertical tectonics of the Australia plate producing rapid and localized uplift in the zone of the active delamination. Also a series of ephemeral sedimentary basins have developed and subsequently been exhumed in the wake of the advancing slab edge. At the southern transition, we argue that the localized subduction of Australia beneath Fiordland is enabled by the progressive tearing of a sliver from the Australian plate. This leaves a newly formed edge to the Australian plate that translates northward along the plate margin becoming the western side of the Alpine Fault plate boundary. It is useful to distinguish between the well-described near-surface Alpine Fault (AF) and the less well understood deeper plate boundary shear zone, which we term the Southern Alps plate boundary (SAPB). As a result of the southward migration of the Hikurangi subduction, the SAPB has been shortening in time. Concurrent with the shortening of the SAPB (since �15 Ma) plate motions between the Pacific and Australia plate have changed, driving a clockwise rotation in the azimuth of motion along the plate boundary through New Zealand. This rotation produces a mismatch between the sense of shear in the ductile lower crust/upper mantle of the plate boundary and the orientation and location of the upper crustal AF. Localization of deformation along the SAPB shear zone can lead to a significant decoupling between the crust and mantle lithosphere. Evidence from upper mantle shear-wave anisotropy (SKS splitting) and deformational modeling suggest that such a decoupling has occurred, and the resulting spatial and temporal variability in crust-mantle coupling across South Island, New Zealand may lead to variability in deformational style along the Southern Alps orogen.
Furlong, K. P.; Kamp, P. J.; Malservisi, R.
Inter- and intra-plate deformation at North American plate boundaries
NASA Technical Reports Server (NTRS)
Alaska tectonics and earthquake hazard studies; Southern California tectonics (block rotation); spreading near the Salton Trough; California plate motion (fault zone kinematics); and Caribbean plate motion investigations are examined.
Beavan, John
Data Access and Web Services at the EarthScope Plate Boundary Observatory
The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five
J. Matykiewicz; G. Anderson; D. Henderson; K. Hodgkinson; B. Hoyt; E. Lee; E. Persson; D. Torrez; J. Smith; J. Wright; M. Jackson
Halfway There: An EarthScope Plate Boundary Observatory Progress Report
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters
M. Jackson; G. Anderson; F. Blume; B. Coyle; K. Feaux; B. Friesen; K. Hafner; M. Hasting; W. Johnson; D. Mencin; B. Pauk; D. Phillips; C. Walls; W. Prescott
Oblique collision and accretion of the Netherlands Leeward Antilles island arc: A structural analysis of the Caribbean-South American plate boundary zone
NASA Astrophysics Data System (ADS)
The Netherlands Leeward Antilles volcanic island arc is an ideal natural laboratory to study the evolution of the Caribbean-South American plate boundary. The Leeward Antilles islands (Aruba, Curacao, and Bonaire) are located offshore western Venezuela, within the obliquely convergent diffuse plate boundary zone. Outcrop analysis, microthermometry, and 2D marine seismic reflection data provide evidence of three generations of regional deformation since the Late Cretaceous. Outcrop analysis of structural features, including faults, joints, and veins, characterizes the kinematic history of the islands. Fluid inclusion analysis of quartz and calcite veins coupled with apatite fission-track dating provides the island exhumation history. Finally, marine reflection seismic data processing and interpretation of newly acquired data elucidates offshore structures to integrate with our onshore results. The oldest regional deformation, resulting in both ductile (D1) and brittle (F 1) structures, is attributed to displacement partitioning along the arcuate Caribbean plate boundary. Associated crustal thinning initiated island exhumation, at a rate of 0.18 km/my, from a maximum burial depth of 6 km in the Late Cretaceous (�89 Ma). Coeval with D1/F1 deformation and exhumation, stretching of the island arc resulted in extensive basin rifting that separated the island blocks. At �55 Ma, a change in the relative motion of the Caribbean plate altered plate boundary dynamics. Displacement along the right-lateral Caribbean transform fault and Oca - San Sebastian - El Pilar strike-slip fault system created a wrench tectonic regime within the diffuse plate boundary zone. A second generation of brittle structures (F2) developed while the islands were at a maximum burial depth of 2 km during the Paleocene/Eocene. Since �45 Ma, continued motion along the strike-slip fault systems and oblique plate convergence resulted in the youngest generation of structural features (F3). Regional tectonics control the ongoing steady-state exhumation of the islands at a rate of 0.04 km/my. Most recently, the northeast escape of the Maracaibo block also drives deformation within the diffuse plate boundary zone. Overall, the Caribbean-South American plate boundary geometry has evolved with diachronous deformation, from west to east, accompanied by 135� of clockwise block rotation during collision and accretion of the Leeward Antilles since the Late Cretaceous.
Beardsley, Amanda Gail
Cenozoic plate tectonic reconstructions and plate boundary processes in the Southwest Pacific
The Australia-Pacific-Antarctic plate circuit has long been a weak link in global plate reconstruction models for Cenozoic time. The time period spanning chron 20 to chron 7 (43-25 Ma) is particularly problematic for global plate models because seafloor spreading was occurring in two poorly constrained regions in the Southwest Pacific - the Macquarie Basin southwest of New Zealand, and the
William R. Keller
Convergence to equilibrium for the Cahn-Hilliard equation with dynamic boundary conditions
NASA Astrophysics Data System (ADS)
This paper is concerned with the asymptotic behavior of solution to the Cahn-Hilliard equation {?u}/{?t}= ??, ?=- ?u-u+u 3, (x,t)??�R +subject to the following dynamic boundary conditions: ? s?||u-? ?u+h s-g su= {1}/{? s} u t, t>0, x??, ? ??=0, t>0, x?? and the initial condition u| t=0=u 0(x), x??, where ? is a bounded domain in R n (n?3) with smooth boundary ? , and ?s>0, ?s>0, gs>0, hs are given constants; ? || is the tangential Laplacian operator, and ? is the outward normal direction to the boundary. This problem has been considered in the recent paper by Racke and Zheng (Adv. Differential Equations 8 (1) (2003) 83) where the global existence and uniqueness were proved. In a very recent manuscript by Pr�ss, Racke and Zheng (Konstanzer Schrift. Math. Inform. 189 (2003)) the results on existence of global attractor and maximal regularity of solution have been obtained. In this paper, convergence of solution of this problem to an equilibrium, as time goes to infinity, is proved.
Wu, Hao; Zheng, Songmu
Understanding LIP formation in relation to lithospheric thickness, plate boundaries and plumes from a global plate tectonic perspective
NASA Astrophysics Data System (ADS)
Large igneous provinces (LIPs) have been defined as either forming in a range of tectonic settings, or predominantly in intraplate tectonic settings. Using plate tectonic reconstructions for the past 200 million years we investigate the relationships between LIP formation, the condition of the underlying lithosphere, and the type and proximity of the closest plume and plate boundaries. We assess >70 continental and oceanic LIPs and ~70 proposed hotspots in the framework of a global plate tectonic model which incorporates dynamically evolving plate boundaries. We investigate (1) the age of the lithosphere LIPs form on (ii) the most likely plume responsible for the formation of each LIP, (iii) differences between the surface expressions of 'deep' versus 'shallow' plumes, and (iv) relationships between active plate boundaries and triple junctions, and LIP formation. A key result of our analysis is that oceanic LIPs, other than seamount chains, form on young oceanic lithosphere (mean age of ~17 million years). We also find that the majority of these oceanic LIPs form within close proximity to hotspots that have previously been classified as originating from deep within the mantle on the basis of criteria such as seismic tomography, isotopic signature, buoyancy and associated seamount chains.
Whittaker, J. M.; Landgrebe, T. C.; Seton, M.; Williams, S.; Matthews, K. J.; M�ller, R.
The Development of the Hayward-Rodgers Creek-Maacama Plate Boundary Fault System
NASA Astrophysics Data System (ADS)
The plate boundary corridor extending from the San Andreas and Hayward faults in central California to the nascent fault system of the northern Maacama fault is developed in response to a fundamental plate boundary change from subduction to translation with the passage of the Mendocino triple junction (MTJ). How this primary plate boundary structure develops in the wake of the MTJ is not clear. The recently acquired GeoEarthScope LiDAR along this plate boundary corridor affords a fresh perspective on the distribution and geometry of active fault segments, as expressed in landscape topography. Using this high-resolution image of the fault system, we are evaluating the manner in which fault segments form, lengthen and coalesce. The resultant dataset of fault segment length, distribution and geometry can be compared to the space-time evolution of the plate boundary in an effort to test competing hypotheses for the localization of shear in a nascent fault system. In particular we are assessing whether this fundamental plate boundary fault system develops by systematic northward propagation in the wake of the MTJ or a more complex pattern of localized patches of fault development coalesce producing a more punctuated development to the faults.
Shi, X.; Furlong, K.; Kirby, E.
Flow Noise Radiation Characteristics of Elastic Plates Excited by Boundary Layer Turbulence.
National Technical Information Service (NTIS)
The investigation treats the problem of sound radiated by an elastic plate, set in an infinite rigid baffle, which vibrates as a result of a turbulent boundary layer pressure field flowing past it. A large highly damped plate can be considered as effectiv...
D. Feit
Turbulent boundary layer pressure field-induced vibrations in a thin flexible plate under water
Two point turbulent boundary layer pressure spectra at the wall were determined empirically in a low noise water tunnel. The measured pressure spectra were used in a linear theory to predict the response of a thin stainless steel rectangular plate attached to the water tunnel. The predicted responses were found to agree well with the measured responses of the plate.
Nilabh Narayan
Turbulent Boundary Layer Pressure Field-Induced Vibrations in a Thin Flexible Plate Under Water
Two point Turbulent Boundary Layer pressure spectra at the wall were determined empirically in a low noise water tunnel. The measured pressure spectra were used in a linear theory to predict the response of a thin stainless steel rectangular plate attached to the water tunnel. The predicted responses were found to agree well with the measured responses of the plate.
Nilabh Narayan
Geodetic measurement of intra-arc deformation in the Philippine Sea-Eurasia plate boundary zone
NASA Astrophysics Data System (ADS)
Recently obtained GPS data in Luzon, Philippines place important constraints on present-day deformation of the Philippine Sea-Eurasia plate boundary zone in the northern Philippine island arc. We use GPS measurements from a 52-station GPS network measured from 1996 - 2001 plus additional 1996-98 GPS measurements reported by Yu et al. [1999] to investigate fault slip rates and possible postseismic deformation following the 1990 Luzon earthquake. The velocity field indicates that the majority of the Philippine Sea - Eurasia plate convergence is taking place west of Luzon, presumably largely at the Manila trench. A relatively small fraction of the convergence appears to be taking place within Luzon or across the East Luzon trough. The major intra-arc deformation is accommodated by strike-slip motion along the Philippine Fault. An elastic half-space model with uniform slip below a sub-surface locking depth yields a slip rate of 40 mm/yr and a locking depth of ~15 km. Significantly smaller (15 +/- 3 mm/yr) geologic estimates of the long-term slip rate along the Digdig segment of the Philippine Fault have been determined from geomorphic offsets and paleoseismic observations [Daligdig, 1997]. In the Bicol Peninsula segment of southeastern Luzon, the geodetic slip rate appears to be somewhat lower, ~25 mm/yr, comparable with the kinematic model of fault slip rate obtained by Barrier et al. (1991) and with geodetic measurements of fault slip further south in Leyte by Duquesnoy et al. (1994). In central Luzon, however, the geological slip rates are significantly smaller than those obtained from GPS measurements. Possible explanations for this discrepancy include (1) systematic errors in the geologic record or unrecognized events in the paleoseismic data base, (2) accommodation of shear strain along a larger number of fault strands than those recognized geologically, or (3) accelerated post-seismic slip along the Philippine Fault in the aftermath of the 1990 earthquake. If the deformation is instead interpreted using an "elastic layer over viscoelastic half-space" model, Beavan et al. (2001) found that the velocity data can be fit well with a lower lithosphere viscosity of 2-3 x 10^19 Pa.s and a long-term slip rate of ~20 mm/yr. To date, however, we find no evidence for decreasing slip rate along the Philippine Fault with time. Detailed measurements in southern Luzon also indicate significant intra-arc deformation west of the Philippine Fault. GPS measurements in southwestern Luzon indicate significant motion within the arc, which could be explained by ~19 mm/yr of left-lateral shear along the "Macolod Corridor" of southwestern Luzon.
Hamburger, M. W.; Bartel, B. A.; Chen, Q.; Corpuz, E.; Beavan, J.
NASA Astrophysics Data System (ADS)
For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.
Baek, Hyung M.; Mix, Adam W.; Giacomin, A. Jeffrey
Inter- and intra-plate deformation at North American plate boundaries
NASA Astrophysics Data System (ADS)
A geodetic network which spans the region between San Francisco and Lake Tahoe has been measured 5 times completely with triangulation in 1880, 1922, 1929, 1943, 1963. A resurvey with the Global Positioning System (GPS) in 1991 allows the formation of 1 coseismic and 4 interseismic epochs. The data from this network provide a unique opportunity to examine the temporal and spatial evolution of the strain field associated with the 1906 San Francisco earthquake in particular and with the Pacific-North American plate boundary in general. Calculations of strain rate from the network data lead to the following conclusions. (1) There is no resolvable (greater than 0.05 microradians/yr) strain in between Sutter Buttes and the Sierra Nevada. (2) Throughout the time since the 1906 earthquake, a region extending at least as far east as the westernmost Great Valley has been undergoing deformation related to Pac:Nam interaction and the associated earthquake cycle. (3) In the time and space of overlap, our results agree with those from the United States Geological Survey (USGS) trilateration data. Both data sets indicate that strain must be accumulating to the east of Vaca. (4) The San Andreas discrepancy cannot be accommodated in the Great Valley at the 1 sigma level of our results. It is possible to absorb it in that region at the 2 sigma level. (5) Strain rate is elevated in the years following the earthquake and decays slowly with time. It is possible that the rate in the Coast Ranges increases until around 1950 and then decays. With the exception of one epoch, strain rate in the Coast Ranges is consistently fault parallel, shows no sign changes, and is consistent with monotonic strain accumulation.
Beavan, John; Gilbert, Lewis E.; Scholz, Chris
Constraints on Lithospheric Rheology from Observations of Seamount-induced Deformation: From the Plate Interiors to Plate Boundaries
NASA Astrophysics Data System (ADS)
Mantle rheology at lithospheric conditions (i.e., temperature < 1200 oC) is important for understanding fundamental geodynamic problems including the dynamics of plate tectonics, subducted slabs, and lithosphere-mantle interaction. Laboratory studies suggest that the rheology at lithospheric conditions can be approximately divided into three different regimes: brittle or frictional sliding, semi-brittle, and plastic flow. However, geodetic, seismic, flexural and mantle dynamic studies of lithospheric deformation suggest that the rheology at plate boundaries may differ significantly from that in plate interiors, and particularly, that plate boundaries may be weakened greatly relative to plate interiors due to yielding and other non-linear effects. In this study, we seek to constrain lithospheric rheology in the plate interiors and at subduction plate boundaries, using observations of deformation at seamounts and oceanic islands caused by volcanic loading. Volcano-induced surface deformation depends critically on lithospheric rheology at the time of seamount and oceanic island emplacement and is not believed to change significantly with time. However, such deformation may change as seamounts and oceanic islands enter a subduction zone, depending on the rheological properties at subduction zones. In an earlier study [Watts and Zhong, 2000], we used the effective elastic thickness at intraplate seamounts inferred from the observations of deformation and gravity to determined effective activation energy of 120 KJ/mol for lithospheric mantle with Newtonian rheology. We have now expanded this study to incorporate non-Newtonian power-law and frictional sliding rheologies, and more importantly, to also include seamounts in subduction zone settings. Our new results suggest that activation energy is significantly smaller than most experimentally determined values for olivine at high temperatures, but may be consistent with more recent experimental results at lithospheric temperatures. We will also present results on modeling seamount-induced deformation in forearc-trench-outer rise regions and discuss their implications for the dynamics of subduction.
Zhong, S.; Watts, A. B.
Experimental Results from a Flat Plate, Turbulent Boundary Layer Modified for the Purpose of Drag Reduction
Recent experiments on a flat plate, turbulent boundary layer at high Reynolds numbers (>10^7) were performed to investigate various methods of reducing skin friction drag. The methods used involved injecting either air or a polymer solution into the boundary layer through a slot injector. Two slot injectors were mounted on the model with one located 1.4 meters downstream of the
Brian R. Elbing
Late Pliocene lamproites from Bucak, Isparta (southwestern Turkey): Implications for mantle �wedge� evolution during Africa-Anatolian plate convergence
NASA Astrophysics Data System (ADS)
Magmatism in the Kirka-Afyon-Isparta (KAI) region, southwestern Turkey, shows a temporal progression from calc-alkaline to ultrapotassic affinity. Magmatic activity is associated with the geodynamic evolution of the 'Isparta Angle' and is typical of a collision-affected convergent plate margin, most magmas being enriched in potassium and other large-ion lithophile elements (LILE) and depleted in high-field strength elements (HFSE) such as Ti, Zr, Nb, Ta, and Hf. However, Late Pliocene ultrapotassic lamproites in the south of 'Isparta Angle' show HFSE-rich incompatible element distributions, similar to those of 'non-orogenic' intraplate leucite basalts (ILB) and oceanic island basalts (OIB). Their association with HFSE-depleted 'orogenic' magmas suggests that ultrapotassic character reflects primarily crustal contamination of their mantle sources, rather than magma-wallrock reaction effects. Their relatively high content of Fe and Ti (for equivalent Mg content), and SiO 2-undersaturated character suggest that they segregated at relatively high pressures (>ca. 2.0 GPa) from fertile sources. In contrast, the older SiO 2-saturated, Afyon (orogenic) magmas which, for equivalent Mg content, show lower contents of Fe and Ti, are better explained as partial melts segregating at ca. 1.0-1.5 GPa from refractory (basalt-depleted) sources, similar to those of basalt-borne xenoliths tapping the lithospheric mantle. The notion of variably fertile contaminated mantle sources is compelling, but needs to be constrained in terms of the dynamic interaction between the lithosphere and asthenosphere and their respective contamination histories. Given the unlikelihood of in situ partial melting of the continental lithosphere mantle, we propose that both orogenic and non-orogenic magmas are generated at different pressures from sources within the convecting asthenosphere, contaminated by both lithospheric mantle and crustal components. This model rests on two testable conjectures: firstly, the interpretation that the continental lithospheric mantle is residual from partial melting at an earlier stage of its history and, secondly, that such material is incorporated into the asthenospheric flow field during and following subduction. The first of these is supported by the ambient compositions of continental basalt-borne xenoliths, while the second is contingent on the prediction that lithospheric mantle may be rheologically transformed during subduction-related hydration prior to its incorporation. The proximity of the Bucak lamproites to the Menderes Massif, a suspected Archean cratonic fragment, highlights the resemblance of these unusual rocks to intra-plate leucite-bearing lamproites elsewhere, whose genesis has been linked to mantle 'wedge convection' triggered beneath cratonic and circumcratonic lithosphere domain boundaries.
�oban, Hakan; Flower, Martin F. J.
Effect of Pressure Gradients on Plate Response and Radiation in a Supersonic Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Using the model developed by the author for zero-pressure gradient turbulent boundary layers, results are obtained for adverse and favorable pressure gradients. It is shown that when a flexible plate is located in an adverse pressure gradient area, it vibrates more than if it were in a favorable pressure gradient one. Therefore the noise generated by the plate in an adverse pressure gradient is much greater than that due to the plate in a favorable pressure gradient. The effects of Reynolds number and boundary layer thickness are also analyzed and found to have the same effect in both adverse and favorable pressure gradient cases. Increasing the Reynolds number is found to increase the loading on the plate and therefore acoustic radiation. An increase in boundary layer thickness is found to decrease the level of the high frequencies and therefore the response and radiation at these frequencies. The results are in good qualitative agreement with experimental measurements.
Frendi, Abdelkader
An active vibration absorber for a flexible plate boundary-controlled by a linear motor
NASA Astrophysics Data System (ADS)
A long, narrow flexible plate subjected to cyclic disturbances at the midsection is regulated by a linear motor at the boundary. Oscillations at the midsection will be eliminated while the rest of the plate is allowed to swing in a way as to counteract the external force. The control design is based on a virtual passive approach without referring to the detailed mathematical model. A vibration absorber integrating the flexible plate with a combination of passive elements attached to the boundary is first devised. Rather than built with hard physical devices, these passive elements including mechanical springs, dampers, and masses are emulated by the linear motor with a suitable feedback law. The feedback signal is the boundary displacement from an LVDT sensor. Numerical simulations illustrate how a node is developed in the middle of the plate while the rest of the structure tends to a harmonic motion. Experimental results confirm the effectiveness of the control scheme.
Wu, Shang-Teh; Chen, Jiann-Yeu; Yeh, Yuan-Chih; Chiu, Yea-Ying
Lithospheric Evolution of the Pacific-North American Plate Boundary Considered in Three Dimensions
NASA Astrophysics Data System (ADS)
Tomographic imaging indicates that the heterogeneity observed in the crust of westernmost North America is underlain by mantle structures of a similar scale and heterogeneity. When likely scaling relationships are used to interpret mantle velocity images, it becomes clear that much of the boundary is explained by mantle lithospheric processes and the crustal evolution is just the surficial expression of strength beneath the surface. The Sierra Nevada block provides something of a Rosetta stone for this interpretation. We note first that Sierra Nevada terrain is not distinguished at the surface from faulted and even shattered batholithic rocks in southern California. It does differ in the upper mantle, because the Sierra Nevada is underlain by a high- velocity root along almost its entire strike. Where that root is missing, roughly south of the White Wolf fault, and east of the Kern Canyon fault, the surface rocks are deforming. The origin of the strong upper mantle component is self-evident near 39.5N latitude, where the contact between the subducting Gorda Slab and the Sierran mantle root can be imaged directly. The upper plate structure dates to latest Mesozoic through Laramide times, with the pattern apparently reinforced on the west to some extent during post-Laramide subduction. Since the genesis of batholithic rocks and the subsequent Laramide history are similar south of the Sierran block, we extrapolate that a similar mantle root would have been present also. This assumption is confirmed with two lines of evidence. First, the mechanical evolution of southern and central California blocks seems to require it. Second, the volumes of the "drips" beneath the Transverse Ranges and southern Sierras exceed reasonable bounds for material scavenged from the mantle lithosphere unless it had distinct initial conditions. The local sources of mantle lithospheric material that could have delaminated around the southern Sierran drip are volumetrically insufficient by a factor of 4 to 7 to account for the drip itself. These problems are resolved if the primary source for southern California drips is Sierran-like mantle roots scavenged from beneath batholithic terrains farther south by dominantly convergence-related plate-boundary processes.
Biasi, G. P.
Long-offset and multi-fold ocean bottom seismographic survey for imaging lithospheric scale structures in plate convergent margins
Recent availability of a large number of ocean bottom seismographs (OBSs), a large volume of air-gun array and a long streamer cable for academics provide several new findings of lithospheric scale structures in plate convergent margins. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has acquired long-offset seismic data using a super-densely deploy OBS (i.e. 1 - 5 km spacing
S. Kodaira; N. Takahashi; A. Nakanishi; G. Fujie; A. Ito; S. Miura; T. Sato; T. Tsuru; Y. Kaneda
Kinematics to dynamics in the New Zealand plate-boundary zone
NASA Astrophysics Data System (ADS)
New Zealand straddles the boundary between the Australian and Pacific plate, with a transition from subduction of Pacific oceanic lithosphere beneath North Island, to oblique continental collision in South Island. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone up to 250 km wide, with displacements on individual faults up to 100s of kilometres. Active deformation must be driven by a combination of plate-boundary forces and internal buoyancy forces. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses, together with simple Airy isostasy, to determine regional crustal and mantle structure. Integration of the vertical normal stress to the base of the deforming layer yields the buoyancy stress. Horizontal gradients of this can be compared with horizontal gradients of strain rate, using the method of England & Molnar (1997), in the context of a simple thin sheet model of deformation. Thus, if deformation is that of a Newtonian fluid, then appropriate combinations of the horizontal gradients of vorticity and dilatation are related to gradients of buoyancy stress by the fluid viscosity. However, the short term geodetic deformation is strongly biased by elastic strain accumulation related to locking on the plate interface, and cannot be used to determine the plate-boundary velocity field averaged over many seismic cycles (see Lamb & Smith 2013). Therefore, I derive here a velocity field for the plate-boundary zone, which is representative of deformation over tens of thousands of years. This is based on an inversion of fault slip, strain rate azimuth and paleomagnetic data, in the context of the short term relative plate motions, solved in a network of triangles spanning the plate-boundary, using the method of Lamb (2000). A comparison of gradients of buoyancy stress with the appropriate combinations of gradients of vorticity and dilatation shows that deformation in the plate-boundary zone does have features that are fluid-like, characterized by a variable viscosity in the range 1 - 10 x 10^21 Pa s. Given the strain rates in the plate-boundary zone, viscosities imply plate-boundary deviatoric stresses < 20 MPa, and are consistent with previous low estimates of shear stresses in subduction zones based on a simple force balance (Lamb 2006). References: England, P.C., and P. Molnar, (1997), Science, 278, 647-649. Lamb, S. (2000), J. Geophys. Res., 105, 25,627-25,653. Lamb, S., (2006), J. Geophys. Res., 111, B07401, doi:10.1029/2005JB003916. Lamb, S., and E. Smith (2013), J. Geophys. Res. Solid Earth, 118, doi:10.1002/jgrb.50221.
Lamb, S. H.
From Slab Window to Plate Boundary: Making the San Andreas Fault System
NASA Astrophysics Data System (ADS)
The development of the San Andreas fault system in the wake of the Mendocino Triple Junction (MTJ) serves as a principal example of processes involved in developing a new plate boundary structure in a slab window environment. The general concepts of slab window formation with MTJ migration, patterns of crustal deformation, and the subsequent development of the major strands of the plate boundary within the shallow slab window corridor are well documented. What is less well understood about the formation of this plate boundary system are the roles of spatial and temporal variations in crustal structure, and slab window volcanics (the northern California Coast Range volcanic centers) in localizing the crustal deformation, constraining the position of the plate boundary fault system, and explaining the slip history of various fault strands along the plate boundary. In particular, we argue that there is a swath or corridor of northern Coast Ranges within which the crust undergoes northward-migrating rapid thinning (aided by the effects of emplaced asthenospheric mantle), whose western margin becomes the Ma'acama/Rodgers Creek/Hayward system. This has specific consequences for both the kinematics of the fault system and the development of slab window volcanism. The localization of upper crustal strain into discrete fault systems (e.g. the Ma'acama and Bartlett Springs Faults) and the initiation of slab-window volcanism are spatially (and thus likely genetically) linked. Such interactions between the emplacement of slab window volcanism, its impact on crustal structure and deformation, and the resulting development of plate boundary fault systems are likely not restricted solely to the San Andreas evolution, but may have played important roles in the development of other segments of the circum-Pacific plate boundary.
Furlong, K. P.
The International Plate Boundary Observatory Chile (IPOC) in the northern Chile seismic gap
NASA Astrophysics Data System (ADS)
Fast convergence between the oceanic Nazca and the continental South American plate is accommodated by recurrent rupture of large segments of the two plates' interface. The resulting earthquakes are among the largest and, for their sizes, most frequent on Earth. Along the Chilean and southern Peruvian margin, all segments have ruptured at least once in the past 150 years for which there exist historic and/or instrumental records. The one segment that is most mature for re-rupture stretches for more than 500 km along the northernmost Chilean coast between roughly -23� and -18� latitude. It last broke in 1877 in a magnitude ~8.8 earthquake, triggering a major Tsunami. From the historical record, it has been known to have a recurrence cycle of approximately 110 years. The adjoining segments to the north and south broke rather recently in 1995 and 2001 in M>8 earthquakes and an M 7.7 earthquake encroached the southern part of the gap in 2007. The IPOC project intends to investigate this segment of the Nazca-South American plate boundary, on which a strong to devastating earthquake is expected to occur within the next years, by monitoring at a variety of time-scales deformation, seismicity, and magnetotelluric fields in the subduction zone at the closing stages of the interseismic cycle before and possibly during occurrence of a big earthquake. For that purpose, installation of long-term observatories in Northern Chile started in 2006 in a close cooperation of the Universidad de Chile (Santiago, Chile), the Universidad Catolica del Norte (Antofagasta, Chile), the Institut de Physique du Globe de Paris (Paris, France), and the German Research Centre for Geosciences (GFZ, Potsdam, Germany). Currently we are operating 14 modern seismological stations equipped with STS-2 broadband seismometers and accelerometers (EPI sensor). At least two more stations will be installed in the near future. To cope with the high resolution and dynamic of the sensors and data acquisition, site installation was accomplished with special care. At each station a cavern was blasted into the bedrock up to 5 meters deep to ensure stable conditions for measurements. Currently five stations are additionally recording continuously GPS signals, another five are also recording meteorological data, and another seven are equipped with Magneto-Telluric (MT) probes (fluxgate magnetometers and electrode lines). It is planned to extend the multi-parameter observation to as many stations as possible. So far ten of the stations are sending continuous data via satellite links (VSAT) to the GEOFON data host at the GFZ. We will be reporting first results on seismicity, transient deformation and MT from the first two years of recording.
Schurr, B.; Asch, A.; Sodoudi, F.; Manzanares, A.; Ritter, O.; Klotz, J.; Chong-Diaz, G.; Barrientos, S.; Villotte, J.-P.; Oncken, O.
Structural architecture of a highly oblique divergent plate boundary segment
The Reykjanes Peninsula in southwest Iceland is a highly oblique spreading segment of the Mid-Atlantic Ridge oriented about 30� from the direction of absolute plate motion. We present a complete and spatially accurate map of fractures for the Reykjanes Peninsula with a level of detail previously unattained. Our map reveals a variability in the pattern of normal, oblique- and strike-slip
Amy E. Clifton; Simon A. Kattenhorn
Kinematics to dynamics in the New Zealand plate-boundary zone
NASA Astrophysics Data System (ADS)
New Zealand straddles the boundary between the Australian and Pacific plate, with a transition from subduction of Pacific plate oceanic lithosphere in the North, beneath North Island to oblique continental collision in South Island. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone up to 250 km wide, with displacements on individual faults up to 100s of kilometres. Here, I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses, together with simple Airy isostasy, to determine the regional crustal and mantle structure. The buoyancy stress in the deforming layer is calculated by integrating the vertical normal stress with depth. This, in combination with plate-boundary stresses, must drive deformation. Horizontal gradients of buoyancy stress can be compared with horizontal gradients of strain rate, using the method of England & Molnar (1997), in the context of a simple thin sheet model of lithospheric deformation. I derive a velocity field for the New Zealand plate-boundary zone, using the method of Lamb (2000). This is representative of deformation over tens of thousands of years, based on fault slip, strain rate azimuth and paleomagnetic data, in the context of the short term relative plate motions. Comparison of appropriate combinations of horizontal gradients of vorticity and dilatation with horizontal gradients of buoyancy stress shows that deformation has some of the features of a Newtonian fluid. In detail, the minima in buoyancy stress, calculated from the vertical density structure, are offset horizontally from that calculated from gradients of strain rate, suggesting strong lateral contrasts in viscosity if deformation is strongly coupled at all levels in the lithosphere, with viscosities in the range 1 - 10 x 10**21 Pa s. However, subduction of Pacific plate lithosphere along the Hikurangi margin, and evidence for underthrusting beneath the Southern Alps, implies decoupling of deformation at depths > 50 km in these regions. In this case, best-fit viscosities for the top 50 km are in the range 1 - 5 x 10**21 Pa s. Given the characteristic strain rates in the plate-boundary zone, all these viscosities imply plate-boundary deviatoric stresses generally < 20 MPa, and are consistent with previous low estimates of shear stresses on the subduction plate interface based on a simple force balance (Lamb 2006). Fluid-like behaviour of the New Zealand plate-boundary zone is consistent with both geodetic data and the observed pattern of shear wave splitting. References: England, P.C., and P. Molnar, Science, 278, 647-649, 1997. Lamb, S., JGR, 105, 25,627-25,653, 2000. Lamb, S., JGR, 111, B07401, doi:10.1029/2005JB003916, 2006.
Lamb, Simon
India and Sunda plates motion and deformation along their boundary in Myanmar determined by GPS
NASA Astrophysics Data System (ADS)
Using a regional GPS data set including �190 stations in Asia, from Nepal to eastern Indonesia and spanning 11 years, we update the present-day relative motion between the Indian and Sundaland plates and discuss the deformation taking place between them in Myanmar. Revisiting measurements acquired on the Main Boundary Thrust in Nepal, it appears that points in southern Nepal exhibit negligible deformation with respect to mainland India. Including these points, using a longer time span than previous studies, and making an accurate geodetic mapping in the newest reference frame allows us to refine the present-day Indian motion. Our results confirm that the current motion of India is slower than predicted by the NUVEL-1A model, and in addition our India-Eurasia motion is significantly (�5 mm/yr) slower than previous geodetic determinations. This new Indian motion, combined with a refined determination of the Sundaland motion, gives way to a relative India-Sunda angular velocity of 20.2�N, 26.1�E, 0.370�/Myr in ITRF2000, predicting a relative motion of 35 mm/yr oriented N10� at the latitude of Myanmar. There, the Sagaing Fault accommodates only 18 mm/yr of right-lateral strike slip, only half of the shear component of motion. We present two models addressing how and where the remaining deformation may occur. A first model of distributed deformation implies convergence on the Arakan subduction (the northern continuation of the now famous Sumatra-Andaman Trench) and wrench faulting in the Arakan wedge. The second model uses localized deformation, where deformation observed west of the Sagaing Fault is entirely due to elastic loading on a faster and oblique Arakan subduction (23 mm/yr). This latter model predicts that a major earthquake of Mw 8.5 may occur every century on this segment of the subduction.
Socquet, Anne; Vigny, Christophe; Chamot-Rooke, Nicolas; Simons, Wim; Rangin, Claude; Ambrosius, Boudewijn
Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere
NASA Technical Reports Server (NTRS)
Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.
Hager, B. H.
Convergence of a non-stiff boundary integral method for interfacial flows with surface tension
NASA Astrophysics Data System (ADS)
Boundary integral methods to simulate interfacial flows are very sensitive to numerical instabilities. In addition, surface tension introduces nonlinear terms with high order spatial derivatives into the interface dynamics. This makes the spatial discretization even more difficult and, at the same time, imposes a severe time step constraint for stable explicit time integration methods. A proof of the convergence of a reformulated boundary integral method for two-density fluid interfaces with surface tension is presented. The method is based on a scheme introduced by Hou, Lowengrub and Shelley [J. Comp. Phys. 114 (1994), pp. 312-338] to remove the high order stability constraint or stiffness. Some numerical filtering is applied carefully at certain places in the discretization to guarantee stability. The key of the proof is to identify the most singular terms of the method and to show, through energy estimates, that these terms balance one another. The analysis is at a time continuous-space discrete level but a fully discrete case for a simple Hele-Shaw interface is also studied. The time discrete analysis shows that the high order stiffness is removed and also provides an estimate of how the CFL constraint depends on the curvature and regularity of the solution. The robustness of the method is illustrated with several numerical examples. A numerical simulation of an unstably stratified two-density interfacial flow shows the roll-up of the interface; the computations proceed up to a time where the interface is about to pinch off and trapped bubbles of fluid are formed. The method remains stable even in the full nonlinear regime of motion. Another application of the method shows the process of drop formation in a falling single fluid.
Ceniceros, H. D.; Hou, T. Y.
Null-Field Integral Equation Approach for Plate Problems With Circular Boundaries
In this paper, a semi-analytical approach for circular plate problems with multiple cir- cular holes is presented. Null-field integral equation is employed to solve the plate prob- lems while the kernel functions in the null-field integral equation are expanded to degen- erate kernels based on the separation of field and source points in the fundamental solution. The unknown boundary densities
Jeng-Tzong Chen; Chia-Chun Hsiao; Shyue-Yuh Leu
Continent-continent collision at the Pacific/Australian plate boundary: Lithospheric deformation, mountain building, and subsequent scientific endeavors
NASA Astrophysics Data System (ADS)
Continental collision occurs at strike-slip plate boundaries where transform motion and oblique convergence create processes of surficial mountain building and deformation within the deeper crust and lithospheric mantle. The Pacific/Australian transform plate boundary in South Island, New Zealand, is characterized by active oblique continent-continent collision with an associated Southern Alps orogen that exhibits both high exhumation rates and rapid strike-slip movement. Beginning in the 1990s, this system was the focus of a decade-long collaborative USA-New Zealand multi-disciplinary study to understand lithospheric structure and processes involved in this transpression. Funded primarily by the NSF Continental Dynamics program and the New Zealand Science Foundation, this project known as SIGHT (South Island Geophysical Transect) with its companion SAPSE (Southern Alps Passive Seismic Experiment) included the following disciplines that involved substantial field observation experiments: seismic reflection, explosion refraction, onshore-offshore wide-angle reflection/refraction, regional and teleseismic passive seismology, magnetotellurics, laboratory petrophysics, gravity, regional geological investigations, and rheological analyses. More than fifty scientists and students from both nations participated in the combined set of studies that have led to over forty-five journal publications, an AGU Monograph, and a dozen graduate theses. Primary results of the project indicate the Pacific-Australian strike-slip plate boundary (Alpine fault) is not vertical but is eastward dipping and rheologically weak based on diverse geophysical data. Most deformation is within the Pacific plate that hosts the Southern Alps orogen. High mantle seismic velocities vertically disposed beneath the orogen suggest Pacific and perhaps Australian mantle lithosphere contribute to a zone of plate-boundary-parallel distributed mantle shortening. The crustal root of the overlying Southern Alps is larger than needed to support surface topography, and is offset from its topographic high, consistent with dynamic thickening of the Pacific crust by the mantle thickening. Teleseismic shear wave splitting is evidence of a wide zone of distributed strain for the mantle portion of the plate boundary. The collective set of results from the South Island projects have led to a number of subsequent studies by various teams, based on follow-up questions, expanded observational expertise, and international collaborative alliances with in particular the New Zealand science community. These studies include a search for the full width of Pacific/Australian distributed mantle strain using marine OBS studies, the transition from strike-slip to plate boundary subduction to the north, the search and discovery of seismic tremor on the Alpine fault, and high resolution geophysical characterization of Alpine fault seismogenesis. The success of geophysically imaging a narrow island using both marine sides led different SIGHT scientists to carry out expanded efforts to study North Island subduction and separately Taiwan mountain building. These efforts benefited and were largely motivated from multi-disciplinary, multi-national collaborations as typically supported by the NSF Continental Dynamics program.
Okaya, D. A.; Stern, T. A.; Davey, F. J.
Intraplate Deformation Adjacent to the Macquarie Ridge South of New Zealand - The Tectonic Evolution of a Complex Plate Boundary
NASA Astrophysics Data System (ADS)
The response of lithospheric plate boundaries to rapid changes in plate motions provide constraints used to determine the manner in which transitions in plate motions and plate boundary configurations can occur. In the case of the Australia - Pacific plate boundary in the Macquarie Ridge region south of New Zealand a substantial change in plate motions has occurred since the Oligocene. Over a period of less than 15Ma, this boundary changed from mid-ocean ridge spreading to simple translation, the record of which is recorded in the fabric and fracture zones of the oceanic lithosphere. Application of available well-constrained plate motions imply that substantial deformation of the oceanic lithosphere must have occurred after fracture zone formation to create the arcuate structure of these fracture zones today. Plate reconstructions of this plate boundary system from the Oligocene through the Early-Mid Miocene are used here to isolate the timing of transitions in plate motion from divergence to translational motion. These reconstructions identify rapid rotations in plate motions after approximately 25Ma. By 20Ma, the majority of crust created along this plate boundary was already in place, and the Australian Plate was translating northwards relative to the Pacific towards New Zealand, where a corner of Australian Plate is ultimately subducted. The timing of this transition in plate motions implies that the onset of subduction at the Puysegur Trench may have been as early as approximately 20Ma. These reconstructions also identify the shape of fracture zones either side of the relic mid-ocean ridge through the time of their formation. Comparison of these restored fracture zones with their present-day appearance delineates a broad zone of deformation extending ~150km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure. This area of deformation coincides with a broad distribution of seismicity in the Australian Plate on both inter- and intra-plate structures, including two great (M8+) earthquakes over the past twenty years, one of which occurred over 130km from the plate boundary. The persistence of this deformation through time indicates a link with the evolution of the plate boundary from divergence to translation and subduction, and may be a result of stress build-up within the Australian Plate as a consequence of the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may act as a resisting force to subduction, and if it continues, further deformation internal to the Macquarie Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate.
Hayes, G. P.; Furlong, K. P.
Analysis of a laminar boundary layer flow over a flat plate with injection or suction
NASA Astrophysics Data System (ADS)
An analysis is performed to study a laminar boundary layer flow over a porous flat plate with injection or suction imposed at the wall. The basic equations of this problem are reduced to a system of nonlinear ordinary differential equations by means of appropriate transformations. These equations are solved analytically by the optimal homotopy asymptotic method (OHAM), and the solutions are compared with the numerical solution (NS). The effect of uniform suction/injection on the heat transfer and velocity profile is discussed. A constant surface temperature in thermal boundary conditions is used for the horizontal flat plate.
Sadri, S.; Babaelahi, M.
Effects of boundary slippage on thin-film lubrication between two nonparallel plane plates
NASA Astrophysics Data System (ADS)
Hydrodynamic lubrications between two plane plates with an intersection angle ? have been investigated using the boundary slippage theory, and relations are obtained between dimensionless pressures and coordinate x, between bearing capacity, friction force, friction coefficient and dimensionless slipping size factor. The results show that bearing capacity of two plane plates without boundary slippage significantly increases with increasing intersection angle ? when 0 < ? < 1�, whereas decreases with increasing intersection angle ? when ? > 1�. The results also show that negative pressure occurs in fluid entrance region and bearing capacity decreases, and friction force and friction coefficient increase with the increase of dimensionless slipping size factor.
Ban, Shu-Hao; Li, Xiao-Yan
Great thrust earthquakes and aseismic slip along the plate boundary of the Makran Subduction Zone
NASA Astrophysics Data System (ADS)
The Makran subduction zone of Iran and Pakistan exhibits strong variation in seismicity between its eastern and western segments and has one of the world's largest forearcs. We determine the source parameters for 14 earthquakes at Makran including the great (Mw 8.1) earthquake of 1945 (the only instrumentally recorded great earthquake at Makran); we determine the loci of seismic and aseismic slip along the plate boundary, and we assess the effects of the large forearc and accretionary wedge on the style of plate boundary slip. We apply body waveform inversions and, for small-magnitude events, use first motions of P waves to estimate earthquake source parameters. For the 1945 event we also employ dislocation modeling of uplift data. We find that the earthquake of 1945 in eastern Makran is an interplate thrust event that ruptured approximately one-fifth the length of the subduction zone. Nine smaller events in eastern Makran that are also located at or close to the plate interface have thrust mechanisms similar to that of the 1945 shock. Seaward of these thrust earthquakes lies the shallowest 70-80 km of the plate boundary; we find that this segment and the overlying accretionary wedge remain aseismic both during and between great earthquakes. This aseismic zone, as in other subduction zones, lies within that part of the accretionary wedge that consists of largely uconsolidated sediments (seismic velocities less than 4.0 km/s). The existence of thrust earthquakes indicates that either the sediments along the plate boundary in eastern Makran become sufficiently well consolidated and de watered about 70 km from the deformation front or older, lithified rocks are present within the forearc so that stick-slip sliding behavior becomes possible. This study shows that a large quantity of unconsolidated sediment does not necessarily indicate a low potential for great thrust earthquakes. In contrast to the east, the plate boundary in western Makran has no clear record of historic great events, nor has modem instrumentation detected any shallow thrust events for at least the past 25 years. Most earthquakes in western Makran occur within the downgoing plate at intermediate depths. The large change in seismicity between eastern and western Makran along with two shallow events that exhibit right-lateral strike-slip motion in central Makran suggest segmentation of the subduction zone. Two Paleozoic continental blocks dominate the overriding plate. The boundary between them is approximately coincident with the transition in seismicity. Although relative motion between these blocks may account for some of the differing seismic behavior, the continuity of the deformation front and of other tectonic features along the subduction zone suggests that the rate of subduction does not change appreciably from east to west. The absence of plate boundary events in western Makran indicates either that entirely aseismic subduction occurs or that the plate boundary is currently locked and experiences great earthquakes with long repeat times. Evidence is presently inconclusive concerning which of these two hypotheses is most correct. The presence of well-defined late Holocene marine terraces along portions of the coasts of eastern and western Makran could be interpreted as evidence that both sections of the arc are capable of generating large plate boundary earthquakes. If that hypothesis is correct, then western Makran could produce a great earthquake or it could rupture as a number of segments in somewhat smaller-magnitude events. Alternatively, it is possible that western Makran is significantly different from eastern Makran and experiences largely aseismic slip at all times. A knowledge of the velocity structure and nature of the state of consolidation or lithification of rocks at depth in the interior portion of the forearc of western Makran should help to ascertain whether that portion of the plate boundary moves aseismically or ruptures in large to great earthquakes. A resolution of this question has important implications for seismic hazard not
Byrne, Daniel E.; Sykes, Lynn R.; Davis, Dan M.
Tectonics of the Scotia-Antarctica plate boundary constrained from seismic and seismological data
NASA Astrophysics Data System (ADS)
The plate boundary between the Scotia and Antarctic plates runs along the broadly E-W trending South Scotia Ridge. It is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs. Seismic profiles and regional-scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern Scotia Sea, and focal solutions from recent earthquakes help to understand the present-day geodynamic setting. The northern edge of the western South Scotia Ridge is marked by a sub-vertical, left-lateral master fault. Locally, a narrow wedge of accreted sediments is present at the base of the slope. This segment represents the boundary between the Scotia plate and the independent South Shetland continental block. Along the northern margin of the South Orkney microcontinent, the largest fragment of the South Scotia Ridge, an accretionary prism is present at the base of the slope, which was possibly created by the eastward drift of the South Orkney microcontinent and the consequent subduction of the transitional crust present to the north. East of the South Orkney microcontinent, the physiography and structure of the plate boundary are less constrained. Here the tectonic regime exhibits mainly strike-slip behavior with some grade of extensional component, and the plate boundary is segmented by a series of NNW-SSE trending release zones which favored the fragmentation and dispersion of the crustal blocks. Seismic data have also identified, along the north-western edge of the South Scotia Ridge, an elevated region - the Ona Platform - which can be considered, along with the Terror Rise, as the conjugate margin of the Tierra del Fuego, before the Drake Passage opening. We propose here an evolutionary sketch for the plate boundary (from the Late Oligocene to the present) encompassing the segment from the Elephant Island platform to the Herdman Bank.
Civile, D.; Lodolo, E.; Vuan, A.; Loreto, M. F.
Do fluids control locking and seismic slip on the subduction fault? - evidence from the Chilean plate boundary
NASA Astrophysics Data System (ADS)
A number of recent studies have suggested that the interseismic locking degree inverted from geodetic data at convergent plate boundaries may be closely related to slip distribution of subsequent megathrust earthquakes as found recently for the Maule 2010 and Tohoku 2011 earthquakes. The physical nature of locking, however, remains a matter of debate. We explore seismic, seismological and geodetic data collected from the southern part of the Maule 2010 earthquake rupture zone - overlapping with the northern termination of the Valdivia 1960 earthquake - in the decade before the event to identify the spatial variability of pore fluid pressure and effective stress along the plate interface zone. The reflection seismic and the seismological data exhibit well defined changes of reflectivity and Vp/Vs ratio along the plate interface that can be correlated with different parts of the coupling zone as well as with changes during the seismic cycle. High Vp/Vs domains, interpreted as zones of elevated pore fluid pressure, spatially correlate with lower locking degree, and exhibit higher background seismicity as expected for partly creeping domains. In turn, unstable slip associated to a higher degree of locking is promoted in lower pore fluid pressure domains. This relationship is particularly well expressed in the upper two thirds of the seismic coupling zone down to a depth of some 25 km at an estimated 250�C. In the gradient zone towards deeper domains locking gradually decreases to very low values, and the elevated Vp/Vs-ratio returns to standard values. At the same time seismic reflectivity remains high to some 35 km and then disappears with only minor S-wave reflectivity persisting down to the zone of intermediate depth seismicity at some 60 km depth that is again highlighted by bright reflections. This transition zone, at temperatures > 250�C is also largely coincident with aftershock clusters and a concentration of geodetically recorded afterslip following the Maule earthquake. From their spatial interrelationship, we suggest similar, but less strongly expressed activity of an overpressured fluid. We demonstrate that variations of pore pressure at the plate interface control locking degree variations and therefore coseismic slip distribution of large earthquakes. Lateral variations of pore fluid pressure may be related to the subduction of a transform zone (Maule fracture zone) responsible for part of the fluid input. Finally, we speculate that pore pressure increase during the terminal stage of a seismic cycle to close to lithostatic pressure with an equivalent reduction of effective strength may be as relevant for earthquake triggering as stress loading from long-term plate convergence.
Oncken, Onno; Moreno, Marcos; Haberland, Christian; Rietbrock, Andreas; Angiboust, Samuel; Bedford, Jon
Simulating the San Andreas Plate Boundary System: Progress and Prospects
NASA Astrophysics Data System (ADS)
Computing the hazard posed by the next large earthquake on the San Andreas fault is best carried out with a simulation-based approach. Here we discuss a numerical simulation, Virtual California, that includes many of the physical processes known to be important in earthquake dynamics. These include elastic interactions among the faults in the model, driving at the correct plate tectonic rates, and frictional physics on the faults using the physics obtained from laboratory models with parameters consistent with the occurrence of historic earthquakes. We report progress on a variety of problems relating to the construction and use of increasingly realistic models for earthquakes on the San Andreas fault system, which will be required as the Working Group on California Earthquake Probabilities moves into its next phase of hazard and risk analysis. One of the important issues is to construct a fault system model based upon current WGCEP data. Here we use Deformation Model 2.2 ( http://www.relm.org/models/WGCEP/ ) to produce the most realistic model to date. We also have more fine-scale versions of previous models, including one model having 3 x 2**12 fault elements. While previous versions of Virtual California used only vertical strike slip faults, we are now incorporating dipping rectangular faults having arbitrary rake anble into the model as well. Versions of the basic code are available in Fortran, C, and object-oriented C++. One of the issues that we have encountered is the existence of a dynamical instability that arises as a direct result of the basic interactions between the fault elements, combined with the requirement that the long term slip rate on all fault elements match the observed field-derived average. Using these new models and simulations, we are engaged in novel types of data assimilation, using a method of "scoring" the simulation in comparison to observed paleoseismic data. In this paper, we summarize these results and discuss the implications for numerical forecasting methods
Rundle, P. B.; Rundle, J. B.; Yakovlev, G.; Fernandez, J.; Shcherbakov, R.; Turcotte, D. L.; Donnellan, A.; Field, N.; Grant, L.; Tiampo, K. F.; van Aalsburg, J.; Kellogg, L. H.
Completion of the 16 station Plate Boundary Observatory (PBO) network on Mt. St. Helens, WA
The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 3 of the installation phase of 852 continuously operating GPS stations in the Western United States. Some of these GPS stations are focused specifically on centers of volcanic activity. Mt. St. Helens is one of these volcanic areas of interest in the Pacific Northwest (PNW)
K. Austin; K. Hafner; K. Fengler; S. Doelger
An upward turbulent bubbly boundary layer along a vertical flat plate
The structure of an upward wall-bounded bubbly flow is investigated in the simple case of a turbulent boundary layer developing on a vertical flat plate. The data reported is part of a research program currently under progress. They concern the void fraction distribution, the wall shear stress, and the mean liquid velocity profiles. It is shown that depending on their
E. Moursali; J. L. Mari�; J. Bataille
Rifting of the plate boundary in North Iceland 1975-1978
A rifting episode started in 1975 on the accreting plate boundary in North Iceland after 100 years of quiescence. Horizontal extension of some 3 m has been observed in the Krafla caldera and the associated 80 km long fissure swarm. The rifting occurs periodically in short active pulses at a few months intervals. Between these active pulses, continuous inflation of
Axel Bj�rnsson; Gunnar Johnsen; Sven Sigurdsson; Gunnar Thorbergsson; Eysteinn Tryggvason
Post-rifting stress relaxation at the divergent plate boundary in Northeast Iceland
Interaction of the elastic lithosphere with the underlying anelastic asthenosphere causes strain to propagate along the Earth's surface in a diffusion-like manner following tectonism at plate boundaries. This process transfers stress between adjacent tectonic segments and influences the temporal tectonic pattern along a plate boundary. Observations of such strain transients have been rare, and have hitherto been confined to strike-slip and underthrusting plate boundaries1. Here we report the observation of a strain transient at the divergent (spreading) plate boundary in Iceland. A Global Positioning System survey undertaken a decade after an episode of dyke intrusion accompanying several metres of crustal spreading reveals a spatially varying strain field with the expected diffusion-pulse shape and an amplitude three times greater than the 5.7 cm that would be expected from the average spreading rate2. A simple one-dimensional model with a thin elastic layer overlying a viscous layer fits the data well and yields a stress diffusivity of 1.1 ?? 0.3 m2 s-1. Combined with struc-tural information from magnetotelluric measurements, this implies a viscosity of 0.3-2 ?? 1019 Pa s - a value comparable to that derived for Iceland from post-glacial rebound23, but low compared with estimates for mantle viscosity obtained elsewhere3.
Foulger, G. R.; Jahn, C. -H.; Seeber, G.; Einarsson, P.; Julian, B. R.; Heki, K.
The Plate Boundary Observatory Borehole Strainmeter Program: Overview of Data Analysis and Products
The PBO borehole strainmeter network is now the largest in the US with 19 strainmeters installed along the Western US Plate Boundary: 14 in the Pacific North West and 5 in Anza, Southern California. With five drilling crews operating though October 2006 the network should grow to 28 strainmeters by December 2006. The areas include Parkfield and Mt St. Helens,
K. Hodgkinson; G. Anderson; M. Hasting; B. Hoyt; M. Jackson; E. Lee; J. Matykiewicz; D. Mencin; E. Persson; S. Smith; D. Torrez; J. Wright
Detection of Slow Slip Events Along the Cascadia Subduction Zone Using Plate Boundary Observatory Borehole Strainmeters
In the spring of 2005, the Plate Boundary Observatory (PBO) began installing borehole strainmeters in the Pacific Northwest. Currently there are 18 borehole strainmeters operating from Vancouver Island, Canada to Southern Oregon that are favorably located to detect slow slip along the Cascadia subduction zone. While the longest (> two weeks) subduction tremor episodes are accompanied by slow slip events,
W. McCausland; E. Roeloffs
Seismotectonics of plate boundaries. Final report, 1 November 1973-30 June 1981
Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.
Berger, J.; Brune, J.N.; Goodkind, J.; Wyatt, F.; Agnew, D.C.; Beaumont, C.
Segmentation of the Aleutian plate boundary derived from stress direction estimates based on fault plane solutions
We propose a new method to investigate stress homogeneity along plate boundaries based on the cumulative misfit of individual fault plane solutions, calculated using assumed stress tensors. Using this method, some segments of faults can be defined, without the time-consuming inversions for stress directions from earthquake fault plane solutions. We assume that the misfits are relatively constant within segments of
Zhong Lu; Max Wyss
Stabilization of Euler-Bernoulli plate equation with variable coefficients by nonlinear boundary feedback
NASA Astrophysics Data System (ADS)
The aim of this paper is to investigate the uniform stabilization of Euler-Bernoulli plate equation with variable coefficients in the principle part subject to nonlinear boundary feedback laws. The exponential or rational energy decay rate is obtained by the multiplier method and the Riemannian geometry method.
Guo, Yuxia; Yao, Pengfei
Tectonic activity and plate boundaries along the northern flank of the Fiji Platform
Recent volcanic activity along the northern flank of the Fiji Platform, revealed for the first time from new GLORIA imagery, suggests that the loci of interplate motion in this region have migrated rapidly since the switch from Vitiaz to New Hebridean subduction at 5�8 Ma. At present the plate boundaries along the northern flank of the Fiji Platform consist of
J. E. Hughes Clarke; P. Jarvis; D. Tiffin; R. Price; L. Kroenke
Accretionary margin of north-western Hispaniola: morphology, structure and development of part of the northern Caribbean plate boundary
Broad-range side-scan sonar (GLORIA) images and single- and multi-channel seismic reflection profiles demonstrate that the margin of north-western Hispaniola has experienced compression as a consequence of oblique North American-Caribbean plate convergence. Two principal morphological or structural types of accretionary wedges are observed along this margin. The first type is characterized by a gently sloping (???4??) sea floor and generally margin-parallel linear sets of sea-floor ridges that gradually deepen towards the flat Hispaniola Basin floor to the north. The ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath Hispaniola. Anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope. In contrast, the second type of accretionary wedge exhibits a steeper (???6-16??) sea-floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin. The internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults. We suggest that changes in sea-floor declivity and internal structure may result from variations in the dip or frictional resistance of the de??collement, or possibly from changes in the cohesive strength of the wedge sediments. The observed pattern of thickening of Hispaniola Basin turbidites towards the insular margin suggests differential southwards tilting of the Hispaniola Basin strata, probably in response to North America-Caribbean plate interactions since the Early Tertiary. Based upon indirect age control from adjacent parts of the northern caribbean plate boundary, we infer a Late Eocene to Early Miocene episode of transcurrent motion (i.e. little or no tilting), an Early Miocene to Late Pliocene period of oblique convergence (i.e. increased tilt) during which the accretionary wedge began to be constructed, and a Late Pliocene to Recent episode of increased convergence (i.e. twice the Miocene to Pliocene tilt), which has led to rapid uplift and erosion of sediment sources on the margin and on Hispaniola, generating a submarine fan at the base of the insular slope. ?? 1992.
Dillon, W. P.; Austin, Jr. , J. A.; Scanlon, K. M.; Terence, Edgar, N.; Parson, L. M.
What drives microplate motion and deformation in the northeastern Caribbean plate boundary region?
NASA Astrophysics Data System (ADS)
north Caribbean plate boundary zone is a broad deformation zone with several fault systems and tectonic blocks that move with different velocities. The indentation by the Bahamas Platform (the "Bahamas Collision") is generally invoked as a cause of this fragmentation. We propose that a second driver of deformation is the western edge of the south dipping Puerto Rico slab moving sideways with the North America plate. The westward motion of the slab edge results in a push on the Caribbean plate farther west. We refer to this second mechanism for deformation as "Slab Edge Push." The motion of the North America plate relative to the Caribbean plate causes both drivers to migrate from east to west. The Bahamas Collision and Slab Edge Push have been operating simultaneously since the Miocene. The question is the relative importance of the two mechanisms. We use mechanical finite element models that represent the two mechanisms from the late Oligocene (30 Ma) to the present. For the present, both models successfully reproduce observed deformation, implying that both models are viable. Back in time the Slab Edge Push mechanism better reproduces observations. Neither mechanism successfully reproduces the observed Miocene counterclockwise rotation of Puerto Rico. We use this rotation to tune a final model that includes fractional contributions of both mechanisms. We find that the Slab Edge Push was the dominant driver of deformation in the north Caribbean plate boundary zone since 30 Ma.
Benthem, Steven; Govers, Rob; Wortel, Rinus
Discovering plate boundaries: Laboratory and classroom exercises using geodetic data to develop students' understanding of plate motion
NASA Astrophysics Data System (ADS)
To introduce the concept of plate boundaries, typical introductory geology exercises include students observing and plotting the location of earthquakes and volcanoes on a map to visually demarcate plate boundaries. Accompanying these exercises, students are often exposed to animations depicting the movement of Earth�s tectonic plates over time. Both of these teaching techniques are very useful for describing where the tectonics plates have been in the past, their shapes, and where the plates are now. With the integration of data from current geodetic techniques such as GPS, InSAR, LiDAR, students can learn that not only have the tectonic plates moved in the past, but they are moving, deforming, and changing shape right now. Additionally, GPS data can be visualized using time scales of days to weeks and on the scale of millimeters to centimeters per year. The familiar temporal and spatial scales of GPS data also help students understand that plate tectonics is a process that is happening in the present and can ease the transition to thinking about processes that are typically described using deep time, a very difficult concept for students to grasp. To provide a more robust learning environment, UNAVCO has been incorporating high-precision GPS data into free, place-based, data-rich learning modules for educators and students in introductory Earth science courses at secondary and undergraduate levels. These modules integrate new scientific discoveries related to crustal deformation and explore applications of GPS, LiDAR, and InSAR techniques to research. They also provide students with case studies highlighting the process of scientific discovery, providing context and meaning. Concurrent to these efforts, tools to visualize the inter-relationships of geophysical and geologic processes, structures, and measurements including high-precision GPS velocity data are an essential part of the learning materials. Among the suite of visualization tools that UNAVCO has made available, the Jules Verne Voyager (JVV) interactive map tools are available online and are very well received by educators in introductory Earth science courses. In response to requests for easily accessible and usable data, UNAVCO built the Data for Educators webpage, incorporating an embedded Google Map with GPS locations and providing current GPS time series plots and downloadable data from the Plate Boundary Observatory. To extend and update the datasets available to our community, UNAVCO has developed a GPS velocity viewer using Google Maps technology and provides a learning- focused KMZ combining geophysical data sets for Google-Earth. By combining near real-time geodetic data with modern visualization tools into inquiry-based learning resources, students are deepening their understanding about the active nature of plate margins and gain a solid foundation for learning future concepts. UNAVCO is a non-profit, membership-governed consortium funded by the National Science Foundation and NASA.
Olds, S. E.
Actively dewatering fluid-rich zones along the Costa Rica plate boundary fault
NASA Astrophysics Data System (ADS)
New 3D seismic reflection data reveal distinct evidence for active dewatering above a 12 km wide segment of the plate boundary fault within the Costa Rica subduction zone NW of the Osa Peninsula. In the spring of 2011 we acquired a 11 x 55 km 3D seismic reflection data set on the R/V Langseth using four 6,000 m streamers and two 3,300 in3 airgun arrays to examine the structure of the Costa Rica margin from the trench into the seismogenic zone. We can trace the plate-boundary interface from the trench across our entire survey to where the plate-boundary thrust lies > 10 km beneath the margin shelf. Approximately 20 km landward of the trench beneath the mid slope and at the updip edge of the seismogenic zone, a 12 km wide zone of the plate-boundary interface has a distinctly higher-amplitude seismic reflection than deeper or shallower segments of the fault. Directly above and potentially directly connected with this zone are high-amplitude, reversed-polarity fault-plane reflections that extend through the margin wedge and into overlying slope sediment cover. Within the slope cover, high-amplitude reversed-polarity reflections are common within the network of closely-spaced nearly vertical normal faults and several broadly spaced, more gently dipping thrust faults. These faults appear to be directing fluids vertically toward the seafloor, where numerous seafloor fluid flow indicators, such as pockmarks, mounds and ridges, and slope failure features, are distinct in multibeam and backscatter images. There are distinctly fewer seafloor and subsurface fluid flow indicators both updip and downdip of this zone. We believe these fluids come from a 12 km wide fluid-rich segment of the plate-boundary interface that is likely overpressured and has relatively low shear stress.
Bangs, N. L.; McIntosh, K. D.; Silver, E. A.; Kluesner, J. W.; Ranero, C. R.; von Huene, R.
Boundary layer flow and heat transfer past a moving plate with suction and injection
NASA Astrophysics Data System (ADS)
The behavior of an incompressible steady boundary layer flow past a permeable semi-infinite flat plate moving in a free stream is discussed in this paper. In addition to the mass transfer from the plate (suction or injection), the viscous dissipation term is also included into the energy equation. The solutions of the transformed ordinary differential equations are obtained numerically using an implicit finite-difference method. The numerical results are given for the velocity and temperature profiles as well as for the skin friction coefficient and the local Nusselt number for various values of the suction/injection parameter ?, ratio of the wall velocity to the free stream velocity parameter ?, Prandtl number Pr and Eckert number Ec. It is found that suction increases the heat transfer by decreasing the thermal boundary layer thickness and the reverse happens for injection. Furthermore, it is also found that the boundary layer equations have non-unique (dual) solutions in some cases.
Ishak, Anuar; Nazar, Roslinda; Pop, Ioan
Measurements of strain at plate boundaries using space based geodetic techniques
NASA Technical Reports Server (NTRS)
We have used the space based geodetic techniques of Satellite Laser Ranging (SLR) and VLBI to study strain along subduction and transform plate boundaries and have interpreted the results using a simple elastic dislocation model. Six stations located behind island arcs were analyzed as representative of subduction zones while 13 sites located on either side of the San Andreas fault were used for the transcurrent zones. The length deformation scale was then calculated for both tectonic margins by fitting the relative strain to an exponentially decreasing function of distance from the plate boundary. Results show that space-based data for the transcurrent boundary along the San Andreas fault help to define better the deformation length scale in the area while fitting nicely the elastic half-space earth model. For subduction type bonndaries the analysis indicates that there is no single scale length which uniquely describes the deformation. This is mainly due to the difference in subduction characteristics for the different areas.
Robaudo, Stefano; Harrison, Christopher G. A.
Late Cenozoic partitioning of oblique plate convergence in the Zagros fold-and-thrust belt (Iran)
The NW trending Zagros fold-and-thrust belt is affected by two major dextral faults: (1) the NW trending Main Recent Fault that accommodates partitioning of oblique convergence at the rear of the western Zagros and (2) the north trending Kazerun Fault located in the central Zagros. Combined structural and fault kinematics studies and SPOT images analysis have shown a Pliocene kinematic
Christine Authemayou; Dominique Chardon; Olivier Bellier; Zaman Malekzadeh; Esmaeil Shabanian; Mohammad Reza Abbassi
Deformation and fluid pressure variation during initiation and evolution of the plate boundary d�collement zone in the Nankai accretionary prism
NASA Astrophysics Data System (ADS)
The plate boundary d�collement zone in the Muroto region of the Nankai accretionary prism records deformation and consolidation histories that have been affected by temporal changes in fluid pressure. Microstructural observations and chemical analysis demonstrate that the d�collement zone initiated in an interval of porous clayey sediments characterized by cementation due to intergranular bonding of authigenic clays. Crosscutting relations of microstructures indicate that the d�collement zone records two compactive deformations. The early compactive deformation involved destruction of porous cemented structure, probably caused by fluid pressure fluctuation. The late compactive deformation was characterized by clay-particle rotation and porosity collapse along the sets of slip surfaces, resulting in zones of preferred orientation of clay particles. These compactive deformations led to significantly higher bulk densities within the d�collement zone compared to the compaction trend of the overlying prism sediments. Elevated fluid pressure following compactive deformations induced an overconsolidated state within the d�collement zone, with fluid-filled dilatant fractures. Bulk density abruptly decreases at the top of the underthrust sediments, but there is no microstructural evidence for cementation. Fluids in the dilated fractures and underconsolidated underthrust sediments are potential sources for the elevated fluid pressure in and below the d�collement zone, resulting in mechanical decoupling of the accretionary prism from underthrust sediments. The fault-fluid interactions in the Muroto region may be applicable to other convergent plate margins where high temperature associated with the subduction of a spreading ridge or hot, young oceanic crust enhances diagenesis and cementation.
Ujiie, Kohtaro; Hisamitsu, Toshio; Taira, Asahiko
Seismic evidence for sharp lithosphere-asthenosphere boundaries of oceanic plates.
The mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics, and thus the understanding of the processes at the lithosphere-asthenosphere boundary (LAB) is fundamental to understand how our planet works. It is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the LAB. Data from borehole broadband ocean bottom seismometers show that the LAB beneath the Pacific and Philippine Sea plates is sharp and age-dependent. The observed large shear wave velocity reduction at the LAB requires a partially molten asthenosphere consisting of horizontal melt-rich layers embedded in meltless mantle, which accounts for the large viscosity contrast at the LAB that facilitates horizontal plate motions. PMID:19390042
Kawakatsu, Hitoshi; Kumar, Prakash; Takei, Yasuko; Shinohara, Masanao; Kanazawa, Toshihiko; Araki, Eiichiro; Suyehiro, Kiyoshi
Discovering Plate Boundaries Update: Builds Content Knowledge and Models Inquiry-based Learning
NASA Astrophysics Data System (ADS)
Discovering Plate Boundaries (DPB) is a jigsaw-structured classroom exercise in which students explore the fundamental datasets from which plate boundary processes were discovered. The exercise has been widely used in the past ten years as a classroom activity for students in fifth grade through high school, and for Earth Science major and general education courses in college. Perhaps more importantly, the exercise has been used extensively for professional development of in-service and pre-service K-12 science teachers, where it simultaneously builds content knowledge in plate boundary processes (including natural hazards), models an effective data-rich, inquiry-based pedagogy, and provides a set of lesson plans and materials which teachers can port directly into their own classroom (see Pringle, et al, this session for a specific example). DPB is based on 4 �specialty� data maps, 1) earthquake locations, 2) modern volcanic activity, 3) seafloor age, and 4) topography and bathymetry, plus a fifth map of (undifferentiated) plate boundary locations. The jigsaw is structured so that students are first split into one of the four �specialties,� then re-arranged into groups with each of the four specialties to describe the boundaries of a particular plate. We have taken the original DPB materials, used the latest digital data sets to update all the basic maps, and expanded the opportunities for further student and teacher learning. The earthquake maps now cover the recent period including the deadly Banda Aceh event. The topography/bathymetry map now has global coverage and uses ice-free elevations, which can, for example, extend to further inquiry about mantle viscosity and loading processes (why are significant portions of the bedrock surface of Greenland and Antarctica below sea level?). The volcanic activity map now differentiates volcano type and primary volcanic lithology, allowing a more elaborate understanding of volcanism at different plate boundaries. The volcanic activity map also now includes seafloor hydrothermal vents to extend the volcanic data set into the oceans. The new maps also more completely represent the polar regions, improving, for example, the students understanding of the ridge system running across the Arctic Sea. We have expanded the teacher�s guide to assist both novice and experienced teachers �see what an Earth Scientist sees� in the data. We have found repeatedly that the real strengths of the DPB activity are that (1) the course materials readily adapt to as well as appropriately challenge all levels of student abilities, leading to very natural differentiated levels of instruction, and (2) students of all levels develop a real ownership in their �plate tectonic� expertise.
Sawyer, D. S.; Pringle, M. S.; Henning, A. T.
Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate)
NASA Technical Reports Server (NTRS)
Recent progress in both the linear and nonlinear aspects of stability theory has highlighted the importance of the receptivity problem. One of the most unclear aspects of receptivity study is the receptivity of boundary-layer flow normal to vortical disturbances. Some experimental and theoretical results permit the proposition that quasi-steady outer-flow vortical disturbances may trigger by-pass transition. In present work such interaction is investigated for vorticity normal to a leading edge. The interest in these types of vortical disturbances arise from theoretical work, where it was shown that small sinusoidal variations of upstream velocity along the spanwise direction can produce significant variations in the boundary-layer profile. In the experimental part of this work, such non-uniform flow was created and the laminar-turbulent transition in this flow was investigated. The experiment was carried out in a low-turbulence direct-flow wind tunnel T-361 at the Central Aerohydrodynamic Institute (TsAGI). The non-uniform flow was produced by laminar or turbulent wakes behind a wire placed normal to the plate upstream of the leading edge. The theoretical part of the work is devoted to studying the unstable disturbance evolution in a boundary layer with strongly non-uniform velocity profiles similar to that produced by outer-flow vorticity. Specifically, the Tollmien-Schlichting wave development in the boundary layer flow with spanwise variations of velocity is investigated.
Kogan, M. N.
Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific
NASA Astrophysics Data System (ADS)
The late Cretaceous to mid Eocene history of the southwest and southernmost Pacific has been subject to starkly contrasting interpretations, ranging from relative tectonic quiescence with the Lord Howe Rise (LHR) being part of the Pacific plate to a dynamic subduction setting. In the first scenario the Tasman Sea would have formed as a consequence of divergence between the Pacific and Australian plates, whereas in the second scenario it would have formed as a marginal basin associated with subduction. The first scenario is supported by a number of arguments, including a lack of evidence for deformation and tectonic activity in New Zealand during this period and a geodynamic modelling inference, namely that the bend in the Hawaiian-Emperor chain can be better reproduced if the LHR is part of the Pacific plate. The second scenario is supported by regional plate kinematic models reconciling a variety of observations including back-arc basin formation and destruction through time and the history of arc-continent collisions. The primary problem with the first scenario is the use of a plate circuit that leaves relative motion between East and West Antarctica unconstrained, leading to an improbable history of periodic compression and extension. The main problem with the alternative scenario is a lack of sampled late Cretaceous volcanic arc rocks east of the LHR. We analysed available geological and geophysical data to constrain the locations of and movements along the plate boundaries in the southwest and southern Pacific from the late Cretaceous to mid Eocene, and assessed how Pacific plate motion is best quantified during this period. Geological and geophysical evidence suggests that a plate boundary separated the Pacific plate from the LHR. The distribution of lower mantle slab material that is imaged by seismic tomography beneath New Zealand is best explained if subduction occurred to the east of the LHR during the entire late Cretaceous to mid Eocene period. Rocks from ophiolitic nappes in the North Island of New Zealand, New Caledonia and Papua New Guinea show evidence of having formed in a back-arc basin during this period, consistent with a subduction zone near the LHR. Although New Zealand is commonly viewed as tectonically quiescent at this time, deformation at several locations to the east and west of the present-day Alpine Fault suggests that a plate boundary cut through Zealandia during Tasman Sea opening. As the LHR was not attached to the Pacific plate and subduction occurred to the east and north of the LHR we suggest that Pacific plate motion is best quantified using a plate circuit through East and West Antarctica, avoiding this zone of southwest Pacific subduction. Future work should focus on better constraining the location of and motion along the late Cretaceous-mid Eocene plate boundary through New Zealand to enable the use of a plate circuit via Australia.
Matthews, Kara J.; Dietmar M�ller, R.; Whittaker, Joanne; Flament, Nicolas; Seton, Maria
Flow around a rotating circular cylinder with an end plate near a plane wall boundary
NASA Astrophysics Data System (ADS)
The objective of the present study is to investigate the characteristics of a flow around a rotating circular cylinder with and without an end plate near a wall boundary. The different cases which are taken into consideration in the current investigations were with gap ratios of 0.1d, 0.5d, 1.0d, 1.5d and 2.0d. A symmetric end plate is attached behind the rotating circular cylinder at a distance of 0.1d from the cylinder and a gap ratio of 1.5d. We performed Computational Fluid Dynamics (CFD) simulation of the flow around a rotating circular cylinder near a plane wall boundary using a CFD solver, STAR-CCM+. Free-stream velocity is kept constant at 5 m/s and the Reynolds number calculated is 3.24X104. We then studied the flow characteristics such as lift and drag generated on the circular cylinder with and without an end plate and the wake structure. We observed that the vortex suppression is increased when the gap ratio is reduced, i.e., when the circular cylinder is nearer to the plane wall boundary. As the gap ratio increases the drag force generated decreases and the lift force increases considerably. In the case of rotating circular cylinder with an end plate, the wake area has moved upwards and the lift generated has increased manifold.
Panchal, Jay K.
Vertical crustal motion of active plate convergence in Taiwan derived from tide gauge, altimetry, and GPS data
NASA Astrophysics Data System (ADS)
Located at the converging junction between the Eurasian and Philippine Sea plates, the island of Taiwan is subject to an active lithospheric deformation as well as seismicity. Taking the difference between the satellite altimetry data (ALT) that give the absolute sea level variation and the tide gauge data (TG) that record the relative sea level variation, we obtain the absolute vertical crustal motion of the tide gauge sites. We use 20 TG stations along the west and east coasts of Taiwan along with the ALT measurements from the TOPEX/Poseidon-Jason satellites in the nearby waters. The ALT-TG results are compared with vertical GPS measurements in discussing vertical motion. We find a general subsidence of the entire Taiwan coast during the past two decades. The west coast sees no prominent vertical motion but with a severe local subsidence due to the over-withdrawal of groundwater. On the east coast, the ALT-TG results in the northern section demonstrate a northward dipping motion. The elastic thickness of the neighboring oceanic lithosphere modeled as an elastic plate with the flexure of the subducting plate shows that the adjacent Philippine Sea plate should be an old, thick oceanic plate, which could drag the slab into the mantle as manifested in a gentle northward subsidence in the northeast Taiwan. In the southern section of the east coast, the ALT-TG results reveal a segmented or undulating pattern in the vertical-motion rates. Judging from the different behaviors between the co-seismic and interseismic vertical motions marked by the major earthquakes during the studied period, we postulate a temporal saw-tooth scenario for the deformation in phases. It demonstrates the opposite motions under different mechanisms in the frontal sections of the subduction zone, which can be understood with lateral collision and slab dragging subject to varied temporal and spatial dependences.
Chang, Emmy T. Y.; Chao, Benjamin F.; Chiang, Chieh-Chung; Hwang, Cheinway
In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds
NASA Technical Reports Server (NTRS)
A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.
Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.
Effects of Boundary Conditions in Laminated Composite Plates Using Higher Order Shear Deformation Theory
NASA Astrophysics Data System (ADS)
This paper extends the applicability of a modified higher order shear deformation theory to accurately determine the in-plane and transverse shear stress distributions in an orthotropic laminated composite plate subjected to different boundary conditions. A simpler, two-dimensional, shear deformable, plate theory accompanied with an appropriate set of through-thickness variations, is used to accurately predict transverse shear stresses. A finite element code was developed based on a higher order shear deformation theory to study the effects of boundary conditions on the behavior of thin-to-thick anisotropic laminated composite plates. The code was verified against three dimensional elasticity results. The study also compared the stresses and deformation results of higher order theory with those obtained using commercial software such as LUSAS, ANSYS and ALGOR. The commercial software are heavily used by designers to design various components/products made of composites. Various combinations of fixed, clamped and simply supported boundary conditions were used to verify a large class of anticipated applications. Results obtained from software are in good agreement for some cases and significantly differ for others. It was found that LUSAS and ANSYS yield better results for transverse deflection and in-plane stresses. But for transverse shear stresses, it is highly dependent on boundary conditions.
Tasneem, Pervez; Khalid, Al-Zebdeh; Al-Jahwari, Farooq K. S.
A Model of Convergent Plate Margins Based on the Recent Tectonics of Shikoku, Japan
Displacements generated by a (viscoelastic finite element) plate tectonic model are compared with and found to be compatible with geodetic survey data taken on the island of Shikoku, Japan. The model indicates that prior to the 1946 Nankaid0 earthquake, large vertical displacements occurred along the continental slope, increasing in magnitude toward and approaching a maximum of 7 m at the
Richard Edward Bischke
MHD Free Convective Boundary Layer Flow of a Nanofluid past a Flat Vertical Plate with Newtonian Heating Boundary Condition
Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement.
Uddin, Mohammed J.; Khan, Waqar A.; Ismail, Ahmed I.
MHD free convective boundary layer flow of a nanofluid past a flat vertical plate with Newtonian heating boundary condition.
Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688
Uddin, Mohammed J; Khan, Waqar A; Ismail, Ahmed I
NSDL National Science Digital Library
This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.
Oberrecht, Kenn
NSDL National Science Digital Library
This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.
Convergence results for pseudospectral approximations of hyperbolic systems by a penalty type boundary treatment
NASA Technical Reports Server (NTRS)
A new method of imposing boundary conditions in the pseudospectral approximation of hyperbolic systems of equations is proposed. It is suggested to collocate the equations, not only at the inner grid points, but also at the boundary points and use the boundary conditions as penalty terms. In the pseudo-spectral Legrendre method with the new boundary treatment, a stability analysis for the case of a constant coefficient hyperbolic system is presented and error estimates are derived.
Funaro, Daniele; Gottlieb, David
Plate Borders and Mountain Building
NSDL National Science Digital Library
This page features animations of four different types of plate boundaries, including one animation of the collision of two pieces of continental crust, forming steep mountain ranges. The animations are all presented in flash, and the plate convergence offers a useful, generic view of orogeny.
Schlumberger Excellence In Educational Development, Inc.
NASA Technical Reports Server (NTRS)
A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.
Engeln, J. F.; Stein, S.
The authors previously investigated the effects of both shear and normal strains in the viscoelastic core layer on modal properties of sandwich plates under hinged boundary conditions. For such boundary conditions, analytic formulation of characteristic equations was possible. Agreeing that most real boundary conditions must lie somewhere between hinged and clamped, it is naturally worthwhile to solve for the clamped
Byung-Chan Lee; Kwang-Joon Kim
The nature of the plate interface and driving force of interseismic deformation in the New Zealand plate-boundary zone, revealed by the continuous GPS velocity field
NASA Astrophysics Data System (ADS)
New Zealand straddles the boundary between the Australian and Pacific plates. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation, with displacements on individual faults up to hundreds of kilometers. However, over periods of several years, GPS measurements show a remarkably smooth pattern of velocities. We show here using a new method of back slip analysis, that almost the entire plate-boundary continuous GPS velocity field can be predicted within measurement error from a simple model of elastic distortion due to deep slip on a single plate interface (megathrust in the Hikurangi and Putsegur subduction zones or fault through continental lithosphere beneath the Southern Alps) at the relative plate motion rates. This suggests that the main driving force of plate-boundary deformation is slip on the deeper moving part of the plate interface, without buried creep in localized shear zones beneath individual surface faults. The depth at which this deep slip terminates (locking point line) determines the width of deformation. Along the Hikurangi margin, there is also clockwise rotation of ~150 km long segment of the fore arc (Wairoa domain) at 4.5� � 1 Ma, relative to the Australian Plate, about a pole in western North Island; model residuals in the velocity field are mainly a result of incomplete averaging of the cycle of slow slip events on the plate interface, downdip of the locking point.
Lamb, Simon; Smith, Euan
World Stress Map Release 2005 - Stress orientations from single focal mechanisms at plate boundaries
NASA Astrophysics Data System (ADS)
The World Stress Map (WSM) is a global compilation of data about recent tectonic stresses from a wide range of indicators (e.g. focal mechanisms, borehole breakouts). It is a valuable tool for the solution of numerous of technological and scientific problems. The orientation of the stress field, for instance, is a primary control on subsurface fluid flow and thus WSM data can be used to improve petroleum production or the efficiency of geothermal power stations. In scientific context, information on the stress state is essential for seismic hazard assessment. The WSM database release 2005 contains more than 14,000 data sets all classified according to a unified quality ranking. Thus, the comparability of data from different types of measurement is guaranteed. The database as well as guidelines and software for plotting stress maps are available free of charge from our website www.world-stress-map.org. Users can create their own stress map including their own stress data almost instantly with the CASMO (Create A Stress Map Online) web tool. Alternatively, users can download the software CASMI (Create A Stress Map Interactively) free of charge and produce their own stress maps. In the WSM 2005 release we refined the definition of so-called Possible Plate Boundary Events (PBE) for stress data from single focal mechanisms (FMS) considering that the orientations of these earthquakes might be rather controlled by the geometry of the plate boundary than by the stress field orientation. In general, it is assumed that numerous randomly oriented faults are present in the crust, so that earthquakes occur on faults optimally oriented relative to the regional stress field. In such a setting the principal axes of the moment tensor (P, B, T) provide good approximations for the principal stress orientations (?_1, ?2, ?3). However, plate boundaries show a different mechanical behavior. They are characterized by faults with preferred orientations and presumably include major faults with a low coefficient of friction which can be easily reactivated. The related P-B-T axes might considerably deviate from ?_1-3 of the regional stress field. We investigate whether this deviation depends on the distance between the FMS and the closest plate boundary segment. We analyze all FMS of the WSM 2005 database release and found that FMS's have a higher potential for large deviations when they meet the following criteria: (1) The tectonic regime of the FMS reflects the plate boundary kinematics. (2) The event is located within a critical distance dcrit relative to its closest plate boundary segment. (3) The deviation between the strike of the nodal plane and the strike of the plate boundary is smaller than 30(�). The critical distances dcrit depends on the type of plate boundaries. We estimate them by means of a statistical analysis with dcrit being 45 km for continental transform faults, 80 km for oceanic transform faults, 70 km for oceanic spreading ridges, and 200 km for subduction zones. The three detection criteria are met by one third of the ~9000 FMS datasets which thus were marked by a PBE flag in the WSM database. Users should be aware that these data might considerably deviate from the regional stress field.
Heidbach, O.; Barth, A.; M�ller, B.; Reinecker, J.; Sperner, B.; Tingay, M.
Geodetic observations in Iceland: divergent plate boundary influenced by a hotspot
NASA Astrophysics Data System (ADS)
The mid Atlantic ridge, separating the Eurasian and North American tectonic plates, is mostly buried below the Atlantic. There are, however, a few places where subaerial exposure of the mid-oceanic rift system allows geodetic observations of the deformation associated with the plate boundary. Iceland is the largest portion of the system emerged above sea level, a consequence of excessive volcanism caused by the interaction of a mantle plume with the mid-oceanic ridge. Iceland is therefore a unique site to study processes associated with divergent plate boundaries, and the effects of the plume-ridge interaction. A network of continuous GPS stations have been operating in Iceland since 1995 when the first station was installed in Reykjavik. Since then, stations have been added to the network at different points in time, with over 70 stations presently in operation. The network has been used e.g. for studies of deformation associated with the divergent plate boundary, micro-plate formation due to rift jumps, the plate-spreading deformation cycle associated with rifting episodes, strain rates and stress accumulation on transform zones connecting the ridge segments and deformation due to magmatic processes. In addition the GPS network is used in studies of the deformation associated with mass variations of Iceland's glaciers. The continuous GPS network serves as monitoring tool in Iceland, both for volcanic and seismic hazards but also as a research tool. In the recent Futurvolc project, which partly builds on EPOS, the data from the continuous GPS network along with data from the seismic network and InSAR observations, will serve as the main input in joint analyses of long and short term magma movements in volcanic regions. The establishment of the continuous GPS network in Iceland has provided an ideal tool to further increase our understanding of the geodynamic processes associated with divergent plate boundaries and plume-ridge interaction as well as establishing a background velocity field, serving as the backbone for detailed geodetic studies of individual processes.
Ofeigsson, Benedikt Gunnar; Hreinsd�ttir, Sigrun; Sigmundsson, Freysteinn; Arnadottir, Thora; Vogfjord, Kristin; Geirsson, Halldor; Einarsson, Pall; Jonsson, Sigurjon; Villemin, Thierry; Fjalar Sigurdsson, Sigurdur; Roberts, Matthew; Sturkell, Erik; Lafemina, Peter C.; Bennett, Richard; Voelksen, Christof; Valsson, Gudmundur; Sigurdsson, Thorarinn
Stress in the lithosphere from non-tectonic loads with implications for plate boundary processes
NASA Astrophysics Data System (ADS)
Stress in the lithosphere from non-tectonic loads is calculated, making use of semi-analytic Fourier models. Sources of non-tectonic stress include coastal lithospheric bending in response to the rise in eustatic sea level since the Last Glacial Maximum, lithospheric rebound and pore pressure changes in response to the intermittent load of Ancient Lake Cahuilla in the Salton trough, stress sustained through the formation and long-term support of local short-wavelength topography, and topography created by the ejecta debris from impact craters on the surface of the icy Galilean satellites. Stresses from time varying surface water loads are calculated along major plate boundaries globally to determine to what extent, if any, these loads influence the major tectonic processes at work in plate boundary regions, such as the earthquake cycle on major faults. It is determined that the stress perturbations from these loads are generally an order of magnitude smaller than the tectonic stress accumulation rate. Their ability to noticeably affect the seismic cycle is therefore restricted to specific circumstances including when the tectonic loading rate is particularly low, such as along secondary plate boundary fault structures, when the nontectonic loading rate is particularly high, such as in the case of catastrophic flooding events, or when the fault in question is already critically stressed to a near-failure level. Stresses from local topography are calculated along the global mid-ocean ridge and along the Chilean subduction megathrust. The predicted orientations of these stresses are compared to a presumed ridge-normal and transform-strike-slip faulting regime or the focal mechanism of a single large earthquake, respectively. Quantitative constraints for the coincident tectonic stresses are subsequently established with implications for the strength of the plate boundary faults and the necessity of particular topographic and bathymetric features.
Luttrell, Karen Marie
Strain accumulation 1986-1992 across the Reykjanes Peninsula plate boundary, Iceland, determined from GPS measurements
Global Positioning System (GPS) geodetic observations 1986-1992 spanning the oblique plate boundary on the Reykjanes Peninsula, SW Iceland, show that left-lateral shear strain is accumulating in the area. The principal strain rates are: dot-epsilon(sub 1) = 0.255 +\\/- 0.055 microstrain\\/yr (extension) at N121 +\\/- 6 deg E, and dot-epsilon (sub 2) = -0.190 +\\/- 0.053 microstrain\\/yr (contraction) at N31 +\\/-
Erik Sturkell; Freysteinn Sigmundsson; Pall Einarsson; Roger Bilham
Plane Wave Diffraction by a Finite Plate with Impedance Boundary Conditions
In this study we have examined a plane wave diffraction problem by a finite plate having different impedance boundaries. The Fourier transforms were used to reduce the governing problem into simultaneous Wiener-Hopf equations which are then solved using the standard Wiener-Hopf procedure. Afterwards the separated and interacted fields were developed asymptotically by using inverse Fourier transform and the modified stationary phase method. Detailed graphical analysis was also made for various physical parameters we were interested in.
Nawaz, Rab; Ayub, Muhammad; Javaid, Akmal
The EarthScope Plate Boundary Observatory Distributed Data Management System
EarthScope is an ambitious multi-year project funded by the United States National Science Foundation to explore the structure and dynamics of the North American continent using a wide range of geophysical methods. The Plate Boundary Observatory (PBO), being built by UNAVCO, is the geodetic component of EarthScope, and will comprise 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters,
G. Anderson; J. Eakins; K. Hodgkinson; J. Matykiewicz; M. Beldyk; B. Blackman; F. Boler; B. Henderson; B. Hoyt; E. Lee; E. Persson; J. Smith; D. Torrez; J. Wright; M. Jackson; C. Meertens
Plate Boundary Observatory Borehole Strainmeter Recordings Of The 29 September 2009 Tsunami
On 29 September 2009 a M8.3 earthquake on the Australian-Pacific plate boundary generated a tsunami that caused widespread damage in Samoa, American Samoa, and Tonga. Peak to trough wave heights of 314 cm were recorded 250 km from the epicenter at Pago-Pago, American Samoa approximately 20 minutes after the event. NOAA's West Coast and Alaska Tsunami Warning Center predicted the
D. B. Henderson; K. M. Hodgkinson; A. A. Borsa; D. Mencin; E. van Boskirk; M. E. Jackson
New Insights into Cascadia Slow Slip Events Using Plate Boundary Observatory Borehole Strainmeters
Until recently, tremor and slow slip events in the Cascadia subduction zone have been recorded only on seismic and GPS networks, respectively. The new Plate Boundary Observatory (PBO) borehole strainmeters record high-sensitivity, high-resolution (20Hz) time series of the horizontal strain fields that result from tremor and slow slip events, much higher than that resolvable from the current GPS network. We
W. A. McCausland; E. Roeloffs; P. Silver
Plate Boundary Observatory Borehole Strainmeter Recordings Of The 29 September 2009 Tsunami
On 29 September 2009 a M8.3 earthquake on the Australian-Pacific plate boundary generated a tsunami that caused widespread damage in Samoa, American Samoa, and Tonga. Peak to trough wave heights of 314 cm were recorded 250 km from the epicenter at Pago-Pago, American Samoa approximately 20 minutes after the event. NOAA's West Coast and Alaska Tsunami Warning Center predicted the
Kathleen Hodgkinson; David Mencin; Adrian Borsa; Mike Jackson
The stability of a three-dimensional laminar boundary layer on a swept flat plate
NASA Technical Reports Server (NTRS)
The linear stability of the laminar boundary layer on a swept flat plate with an imposed favorable pressure gradient was studied utilizing a linear stability model which accounts for streamline curvature for three-dimensional incompressible flows. Calculations were performed for an effective leading-edge sweep angle of 42.5 degrees and freestream velocity of 19 m/s. Computed disturbance amplification rates for the spectrum of amplified frequencies and wavelengths for stationary crossflow vortices were compared with experimental results.
Collier, F. S., Jr.; Mueller, B.; Bippes, H.
Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid
This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ? ? < ?. Flow properties of the viscoelastic fluid are discussed through graphs.
Mehmood, Ahmer; Ali, Asif; Saleem, Najma
High-Reynolds-number flat-plate turbulent boundary layer measurements
A set of experiments was conducted in the U.S. Navy's Large Cavitation Channel (LCC) into the characteristics of a liquid turbulent boundary layer at nearly zero-pressure-gradient. The hydraulically smooth, k^+ < 0.2, flat-plate test model measured 12.9 m in length and 3.05 m in span and was approximately centered in the LCC test section. Data was gathered at flow speeds
Eric S. Winkel; James M. Cutbirth; Marc Perlin; Steven L. Ceccio; David R. Dowling
Coseismic slip resolution along a plate boundary megathrust: The Nankai Trough, southwest Japan
Geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 Tonankai (Mw=8.1) and 1946 Nankaido (Mw=8.3) earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust. Data used include 798 angle changes from triangulation surveys, 328 leveling section differences, and 5 coseismic tidal gage offsets. Many of the
Takeshi Sagiya; Wayne Thatcher
Transition of the boundary layer on a flat plate at supersonic and hypersonic velocities
The transition of the boundary layer from the laminar to the turbulent state on a smooth flat plate at a zero angle of attack\\u000a is studied in the range of Mach numbers M? = 2�6. It is demonstrated that the results measured at the end of the transition region can be approximated by a simple dependence\\u000a suitable for applications, which
V. I. Kornilov; SB RAS
Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model
We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions\\/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 h, on the background seismic process, in case of
L. Petrova; B. Pavlov
Influence of convergent plate boundaries on upper mantle flow and implications for seismic anisotropy
Shear-wave splitting observations in the region of the upper mantle enveloping subduction zones have been interpreted as showing extensive regions of trench-parallel flow, despite the difficulty of reconciling such behavior with a sound model based on the forces that drive mantle motion. To gain insight into the observations, we systematically investigate flow patterns around the cold downwelling sheets associated with
Julian P. Lowman; Laura T. Pinero-Feliciangeli; J.-Michael Kendall; M. Hosein Shahnas
Raman scattering measurements within a flat plate boundary layer in an inductively coupled plasma wind tunnel
High temperature air chemistry is a crucial issue concerning next reusable space vehicle thermal protection system. The aim of this paper is to measure N{sub 2} and O{sub 2} densities and characteristic temperatures thanks to spontaneous Raman scattering within the boundary layer of a stainless steel flat plate cooled down at 300 K. This shear-flow test configuration is considered as a nonequilibrium air plasma test case. Vibrational and rotational temperatures are determined by comparing experimental spectra with computed ones. The density calculation is performed using the ratio of first vibrational transition intensities for both cases with and without plasma at 38 hPa. Several sections were investigated between 15 and 40 mm from the leading edge. All these sections exhibit a classical boundary layer pattern. The rotational temperature is completely in equilibrium with the plate and reaches 2500 K at the outer edge of the boundary layer. On the contrary, the vibrational temperature drops to 1500 K near of the plate and is about 5000 K in the freestream. Molecular densities are smaller than expected at equilibrium, about 60% of the equilibrium value in the freestream for N{sub 2}.
Studer, Damien; Vervisch, Pierre [UMR 6614-CORIA, Technopole du Madrillet, BP12, Avenue de l'Universite, 76801 Saint Etienne du Rouvray, Cedex (France)
Preservation of contrasting geothermal gradients across the Caribbean-North America plate boundary (Motagua Fault, Guatemala)
NASA Astrophysics Data System (ADS)
Strike-slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures. Thermo-kinematic modeling of this type of strike-slip plate boundary predicts an asymmetric signature in the low-temperature thermochronologic record across the fault. Age-elevation profiles of zircon (U-Th)/He ages across the Motagua Fault, a 500 km long segment of the transform boundary between the North American and Caribbean plates, document a sharp cooling age discontinuity across the fault. This discontinuity could be interpreted as a difference in denudation history on each side of the fault. However, a low-relief Miocene erosional surface extends across the fault; this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault. By integrating magmatic, volcanic, and heat flow data, age-elevation profiles, and thermo-kinematic modeling, we propose that large horizontal displacement along the Motagua Fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age-elevation patterns. This study illustrates how thermochronology can be used to detect large strike-slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results.
Simon-Labric, Thibaud; Brocard, Gilles Y.; Teyssier, Christian; Beek, Peter A.; Fellin, Maria Giuditta; Reiners, Peter W.; Authemayou, Christine
Turbulent Boundary Layer Separation Induced over a Flat Plate by a Rotating Cylinder
NASA Astrophysics Data System (ADS)
A novel technique to generate and control an adverse pressure gradient (APG) over a flat plate was implemented by using a rotating cylinder for the purpose of studying turbulent boundary layer (TBL) separation. For this experiment, a flat plate and a fixed diameter cylinder were mounted vertically in a water tunnel to investigate the flow field where the boundary layer was tripped to the turbulent state. Variability in the strength of the APG induced on the plate was achieved using the rotation speed of the cylinder. Digital Particle Image Velocimetry (DPIV) was used to investigate the nature and extent of TBL separation induced by the cylinder rotation. Moreover, a theoretical, inviscid flow calculation of the pressure coefficient induced by the rotating cylinder on the flat plate was performed to predict the strength of the APG. Location of separation, percentage mass flow reversal, and length of the separated flow region were all analyzed as a function of the Reynolds number and strength of the APG.
Afroz, Farhana; Jones, Emily; Smith, Drew; Wheelus, Jennifer; Lang, Amy
Plate boundary reorganization in the active Banda Arc-continent collision: Insights from new GPS measurements
NASA Astrophysics Data System (ADS)
New GPS measurements reveal that large sections of the SE Asian Plate are progressively accreting to the edge of the Australian continent by distribution of strain away from the deformation front to forearc and backarc plate boundary segments. The study was designed to investigate relative motions across suspected plate boundary segments in the transition from subduction to collision. The oblique nature of the collision provides a way to quantify the spatial and temporal distribution of strain from the deformation front to the back arc. The 12 sites we measured from Bali to Timor included some from an earlier study and 7 additional stations, which extended the epoch of observation to ten years at many sites. The resulting GPS velocity field delineates at least three Sunda Arc-forearc regions around 500 km in strike-length that shows different amounts of coupling to the Australian Plate. Movement of these regions relative to SE Asia increases from 21% to 41% to 63% eastward toward the most advanced stages of collision. The regions are bounded by the deformation front to the south, the Flores-Wetar backarc thrust system to the north, and poorly defined structures on the sides. The suture zone between the NW Australian continental margin and the Sunda-Banda Arcs is still evolving with more than 20 mm/yr of movement measured across the Timor Trough deformation front between Timor and Australia.
Nugroho, Hendro; Harris, Ron; Lestariya, Amin W.; Maruf, Bilal
What controls the shallow structure of divergent plate boundaries? Insights from field and modelling data
NASA Astrophysics Data System (ADS)
The interest in the role of magma in splitting plates at divergent plate boundaries through discrete rifting episodes has been re-invigorated. However, despite the renewed enthusiasm for this topic, the precise mechanism by which the magma affects the geometry, the kinematics, and the temporal evolution of a rift is still poorly understood. Here we address several of the related issues, focusing on the surface deformation along plate boundaries, and then comparing the observed deformation with the results of analogue models on dike intrusion. We investigated surface deformation at divergent plate boundaries via field surveys in the Neovolcanic Zone of Iceland and the Main Ethiopian Rift, with focus on: 1) single eruptive fissures (Laki and Eldgj�, South Iceland), 2) mature rifts where several diking events have occurred comparatively recently (i.e. Sveinagj� and Krafla in North Iceland and Fantale in Ethiopia) and 3) on fissure swarms where strike-slip component is also present (Vogar and �ingvellir swarms, Southwest Iceland). Systematic measurements of fault and extension-fracture geometries and kinematics were carried out, including the analysis of the morphology of the fault terminations as possible indicators of the propagation direction of the faults. In addition, we conducted measurements across the fossil �lftafj�r�ur dyke swarm, of late Tertiary age, in East Iceland, exposed at a depth of about 1.2 km below the original surface of the rift zone within which the dikes were emplaced. We use this dataset to calculate the crustal dilation due to diking and faulting at depth at 1-2 km. Analogue models are used as a complementary tools to aid understanding of the geometry and the kinematics of dike-induced structures, under systematically varied boundary conditions (intrusion depth, number of dikes per unit length of profile, etc). Laser-scanner and Particle Image Velocimetry (PIV) techniques were used to quantify the surface deformation in the analogue models and to reconstruct the time evolution of the rift-zone development. The field and analogue results make it possible to provide a general model which considers the role of tectonics and magma (diking) in the development of the axial part of divergent plate boundaries.
Trippanera, Daniele; Acocella, Valerio; Ruch, Joel; Abebe, Bekele; Norini, Gianluca; Thordarson, Thor; Urbani, Stefano; Gudmundsson, Agust
Plate boundary deformation at the latitude of the Salton Trough - northern Gulf of California (Invited)
NASA Astrophysics Data System (ADS)
Along the Pacific-North America plate boundary zone, the segment including the southern San Andreas fault to Salton Trough and northern Gulf of California basins has been transtensional throughout its evolution, based on Pacific-North America displacement vectors calculated from the global plate circuit (900 � 20 km at N54�W since 20 Ma; 460 � 20 km at N48�W since 11 Ma). Nevertheless, active seismicity and focal mechanisms show a broad zone of plate boundary deformation within which the inferred stress regime varies locally (Yang & Hauksson 2013 GJI), and fault patterns in some regions suggest ongoing tectonic rotation. Similar behavior is inferred to have occurred in this zone over most of its history. Crustal structure in this region is constrained by surface geology, geophysical experiments (e.g., the 2011 Salton Seismic Imaging Project (SSIP), USGS Imperial Valley 1979, PACE), and interdisciplinary marine and onland studies in Mexico (e.g., NARS-Baja, Cortes, and surveys by PEMEX). Magnetic data (e.g., EMAG-2) aids in the recognition of large-scale crustal provinces and fault boundaries in regions lacking detailed geophysical surveys. Consideration of existing constraints on crustal thickness and architecture, and fault and basin evolution suggests that to reconcile geological deformation with plate motion history, the following additional factors need to be taken into account. 1) Plate boundary displacement via interacting systems of rotating blocks, coeval with slip on steep strike slip faults, and possibly related to slip on low angle extensional faults (e.g, Axen & Fletcher 1998 IGR) may be typical prior to the onset of seafloor spreading. This fault style may have accommodated up to 150 km of plate motion in the Mexican Continental Borderland and north of the Vizcaino Peninsula, likely between 12 and 15 Ma, as well as explaining younger rotations adjacent to the Gulf of California and current deformation southwest of the Salton Sea. 2) Geophysical characteristics suggest that the zone of strike-slip faults related to past plate boundary deformation extends eastward into SW Arizona and beneath the Sonoran coastal plain. 3) 'New' crust and mantle lithosphere at the plate boundary, in the Salton Trough and the non-oceanic part of the northern Gulf of California, varies in seismic velocity structure and dimensions, both within and across extensional segments. Details of within-segment variations imaged by SSIP (e.g., Ma et al., and Han et al., this meeting) are attributed to active fault patterns and small scale variations in hydrothermal activity and magmatism superposed on a more uniform sedimentation. Differences between the Imperial Valley rift segment and the north Gulf of California segments may be due to more involvement of low angle normal faults in the marine basins in the south (Martin et al., 2013, Tectonics), as well as differences in lower crustal or mantle lithospheric flow from the adjacent continental regions.
Stock, J. M.
The Convergence of Spectral and Finite Difference Methods for Initial-Boundary Value Problems
The general theory of compatibility conditions for the differentiability of solutions to initial-boundary value problems is well known. This paper introduces the application of that theory to numerical solutions of partial differential equations and its ramifications on the performance of high-order methods. Explicit application of boundary conditions (BCs) that are independent of the initial condition (IC) results in the compatibility
Natasha Flyer; Paul N. Swarztrauber
Seismotectonics of the Lwandle-Nubia plate boundary between South Africa and the Southwest Indian Ridge
NASA Astrophysics Data System (ADS)
The Lwandle (LW) plate shares a boundary with the Nubia (NU) plate, extending from a diffuse triple junction with the Rovuma plate in Southern Mozambique to a triple junction with the Antarctic plate along a segment of the Southwest Indian Ridge (SWIR). The LW-NU boundary terminates in the ~750 km-long, complex transform of the Andrew Bain Fracture Zone (ABFZ), but its exact locus is still unclear. Recent works locate it along the eastern boundary of the submarine Mozambique Ridge, parallel to the pre-existing, oceanic transform-fault fabric. However, an early concept of the LW block ('ambiguous region' of Hartnady, 1990, Fig. 2) indicates a more westerly trajectory in the north that includes parts of South Africa, with a southerly extension across old oceanic crust of the submarine Natal Valley and Transkei Basin. This proposed boundary is marked by several, aligned epicentres of moderate to strong earthquakes (1941, 1942, 1956, 1969, 1972, 1975, 1981 and 1989). Our re-examination of seismographic records from the 1975 'intraplate' earthquake (-37.62�N, 30.98�E, mb5.0), in the oceanic crust of the distal Transkei Basin, shows a thrust-faulting focal mechanism along a nodal plane striking N272�E. The largest (ML4.2) of a series of three small earthquakes in the Natal Valley in 2009, close to a zone of recent seafloor deformation mapped in 1992, has similar first-motion patterns at Southern African seismograph stations. When the 1975 slip-vector result (N173�E) is combined with a normal-faulting slip vector (N078�E) from a 1986 onland earthquake (-30.53�N, 28.84�E, mb5.0) near the Lesotho-KZN border, and both are incorporated into the wider data-set previously used to solve for East African Rift kinematics, they produce a LW-NU rotation pole that is located south of Africa, near the Agulhas Plateau, and approximately 950 km from the Natal Valley deformation zone. The modeled low rate of right-lateral, LW-NU slip (~0.50-0.75 mm/yr) across this LW-NU boundary segment suggests that the 1972, 1981 and nearby 2009 earthquakes are instances of a 'long aftershock sequence' in the source zone of the 1850 'i-Nyikima' event, which was felt over a very wide region of the Eastern Cape Colony, and the adjacent territories of British Kaffraria and Pondoland. This remarkable historic shaking appears to have been caused by a great (Mw8.0+), oceanic event along a segment of the LW-NU boundary, resembling the 1942 SWIR event along the ABFZ and the recent (2012 March 11) North Indian Ocean events along the incipient boundary between the Indian and Australian plates. This new interpretation has implications for the re-assessment of seismic and submarine-landslide (tsunami) hazard along the SE continental margin of South Africa. Reference Hartnady CJH (1990). Seismicity and plate boundary evolution in southeastern Africa. S. Afr. J. Geol. 93, 473 484.
Hartnady, Chris; Okal, Emile; Calais, Eric; Stamps, Sarah; Saria, Elifuraha
Geodynamic modeling of passive margin systems from tectonic reconstructions with deforming plate boundaries
NASA Astrophysics Data System (ADS)
The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate reconstructions, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of Euler poles for rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the rigid blocks within continents; (2) a definition of the regions in which continental crust deformed between these blocks. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along conjugate passive margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate continent/ocean boundaries (COBs). Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend forward in time as the major rigid plates drift apart. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. The velocity field derived from the plate reconstructions is used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. In deforming areas, the velocity field is obtained by linearly interpolating velocities from adjacent non-deforming areas within GPlates. We computed forward global mantle flow models using 3D-spherical finite-element code CitcomS to simultaneously quantify the relative contributions of lithospheric stretching, thermal subsidence, and deep mantle flow to the subsidence of passive margins. Applied to the South Atlantic, the method reproduces the first-order asymmetry of the margins. In particular, the large subsidence of the Argentinian margin is due to the dynamic topography induced by ongoing subduction along the narrow southern portion of South America. This result illustrates the importance of dynamic topography to the total subsidence at passive margins.
Williams, S.; Flament, N.; Heine, C.; Hosseinpour Vazifehshenas, M.; Seton, M.; Gurnis, M.; M�ller, R. D.
Transients in Pacific/North American Plate Boundary Deformation: Synthesis and Modeling of GPS and Borehole Strain Observations.
National Technical Information Service (NTIS)
This is the Final Technical Report on research conducted between 1 June 1997 and 14 September 2001 entitled 'Transients in Pacific/North American plate boundary deformation: Synthesis and modeling of GPS and borehole strain observations.' As the project t...
S. C. Solomon
The 2000 Mw 6.8 Uglegorsk earthquake and regional plate boundary deformation of Sakhalin from geodetic data
Interseismic GPS velocities in Sakhalin indicate that the island moves to the west at 3�4 mm\\/yr with respect to the Eurasian plate, which is about half of the relative Eurasia - North America plate convergence rate. GPS measurements across the central Sakhalin fault system provide evidence of compressive and strike-slip strain accumulation at a rate ?3 mm\\/yr. Coseismic vertical displacements
M. G. Kogan; R. B�rgmann; N. F. Vasilenko; C. H. Scholz; R. W. King; A. I. Ivashchenko; D. I. Frolov; G. M. Steblov; Ch. U. Kim; S. G. Egorov
First epoch geodetic measurements with the Global Positioning System across the northern Caribbean plate boundary zone
NASA Technical Reports Server (NTRS)
The first geodetic survey across the northern Caribbean plate boundary zone with GPS was conducted in June 1986. Baseline vectors defined by the six-station regional GPS network ranged from 170 to 1260 km in length. Repeatability of independent daily baseline estimates was better than 8 mm plus 1.3 parts in 10 to the 8th of baseline length for horizontal components. The wet tropospheric path delay during the experiment was both high, sometimes exceeding 30 cm at zenith, and variable, sometimes exceeding 5 cm variation over several hours. Successful carrier phase cycle ambiguity resolution (bias fixing) could not be achieved prior to construction of a regional troposphere model. With optimum troposphere treatment and single-day orbital arcs, most biases on baselines were resolved up to about 550 km in length. With multiday orbital arcs most biases in the network were resolved regardless of baseline length. The results suggest that constraints on plate-boundary zone deformation in the Greater Antilles, and on the North America-Caribbean relative plate motion vector, can be obtained with a series of GPS experiments spanning less than 10 and 15 years, respectively.
Dixon, T. H.; Gonzalez, G.; Lichten, S. M.; Katsigris, E.
The boundary between the Indian and Asian tectonic plates below Tibet.
The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567
Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei
The boundary between the Indian and Asian tectonic plates below Tibet
The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660�km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.
Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei
Quasi-simultaneous interaction method for solving 2D boundary layer flows over plates and airfoils
NASA Astrophysics Data System (ADS)
This paper studies unsteady 2D boundary layer flows over dented plates and a NACA 0012 airfoil. An inviscid flow is assumed to exist outside the boundary layer and is solved iteratively with the boundary layer flow together with the interaction method until a matching solution is achieved. Hereto a quasi-simultaneous interaction method is applied, in which the integral boundary layer equations are solved together with an interaction-law equation. The interaction-law equation is an approximation of the external flow and based on thin-airfoil theory. It is an algebraic relation between the velocity and displacement thickness. The interaction-law equation ensures that the eigenvalues of the system of equations do not have a sign change and that no singularities occur. Three numerical schemes are used to solve the boundary layer flow with the interaction method. These are: a standard scheme, a splitting method and a characteristics solver. All schemes use a finite difference discretization. The three schemes yield comparable results for the simulations carried out. The standard scheme is deviating most from the splitting and characteristics solvers. The results show that the eigenvalues remain positive, even in separation. As expected, the addition of the interaction-law equation prevents a sign change of the eigenvalues. The quasi-simultaneous interaction scheme is applicable to the three numerical schemes tested.
Bijleveld, H. A.; Veldman, A. E. P.
Relaxation of an unsteady turbulent boundary layer on a flat plate in an expansion tube
NASA Technical Reports Server (NTRS)
An analysis is presented for the relaxation of a turbulent boundary layer on a semi-infinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion-tube flows. The flow-governing equations have been transformed into the Crocco variables, and a time-similar solution is presented in terms of the dimensionless distance-time variable alpha and the dimensionless velocity variable beta. An eddy-viscosity model, similar to that of time-steady boundary layers, is applied to the inner and outer regions of the boundary layer. A turbulent Prandtl number equal to the molecular Prandtl number is used to relate the turbulent heat flux to the eddy viscosity. The numerical results, obtained by using the Gauss-Seidel line-relaxation method, indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin friction than a laminar boundary layer. The results also give a fairly good estimate of the local skin friction and heat transfer for near steady-flow conditions.
Gurta, R. N.; Trimpi, R. L.
The turbulent boundary layer and wake of an aligned flat plate
NASA Astrophysics Data System (ADS)
A theoretical study of the turbulent boundary layer and symmetric wake of an aligned flat plate is described. A specific turbulence model is taken throughout, namely the Cebeci-Smith (1974) one, although at the high Reynolds numbers of interest the wake results are found subsequently to be influenced hardly at all by the precise details of the model, so that there is a ready generalization. The two-tiered wake implied by the analysis is rather different from the two-tiered boundary layer. The inner tier of the wake is thicker than the boundary layer's inner tier and, associated with this, the 'logarithmic' zone present in the boundary layer upstream is absent in the wake, being replaced by a 'cuspidal' zone just outside the inner-wake tier due to the reduction in shear stresses. Local interactive regions near the trailing edge show how the erosion of the logarithmic behavior takes place relatively fast, being virtually complete on entry into the full wake. The agreement between the theory, experiments and previous computations for the boundary layer and full wake is found to be good quantitatively as well as qualitatively, encouraging the use of the present approach in other contexts such as turbulent separation.
Neish, A.; Smith, F. T.
Prehistoric earthquakes on the Caribbean-South American plate boundary, central range fault, Trinidad
Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9-15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7). ?? 2010 Geological Society of America.
Prentice, C. S.; Weber, J. C.; Crosby, C. J.; Ragona, D.
Prehistoric earthquakes on the Caribbean-South American plate boundary, central Range Fault, Trinidad
Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9�15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7).
Carol S Prentice; Christopher J Crosby; Weber, John C.; Ragona, Daniel
Plate Boundary Observatory Borehole Strainmeter Recordings Of The 29 September 2009 Tsunami
NASA Astrophysics Data System (ADS)
On 29 September 2009 a M8.3 earthquake on the Australian-Pacific plate boundary generated a tsunami that caused widespread damage in Samoa, American Samoa, and Tonga. Peak to trough wave heights of 314 cm were recorded 250 km from the epicenter at Pago-Pago, American Samoa approximately 20 minutes after the event. NOAA�s West Coast and Alaska Tsunami Warning Center predicted the tsunami would arrive at Tofino, Vancouver Island, British Columbia, at 05:12 UTC, 30 September 2009. Tide gauges at Tofino recorded a 7.3 cm amplitude wave arriving at 05:45 UTC. As part of the Plate Boundary Observatory, UNAVCO has installed 74 borehole tensor strainmeters along the western United States for the purpose of recording short-term strain transients associated with plate boundary deformation. Two of these strainmeters, Ucluelet and Bamfield, are located on the west coast of Vancouver Island within a few hundred meters of the Pacific shore line. A third, Port Alberni, is located at the north-east end of Port Alberni Inlet, ~ 50 km inland. The strainmeters at Ucluelet and Bamfield recorded strain signals associated with the arriving tsunami at times consistent with arrival times recorded by tide gauges at Tofino and Bamfield, ~05:45 UTC. A much smaller signal is recorded about 10 minutes later at Port Alberni. The largest strain signals were recorded at Ucluelet between 06:19 and 06:24 UTC. For this study we document the arrival times, nature and frequency content of the tsunami signal as recorded by PBO strainmeters on Vancouver Island and compare these strain measurements against the crustal loading signature predicted by water height changes at nearby tide gauges.
Henderson, D. B.; Hodgkinson, K. M.; Borsa, A. A.; Mencin, D.; van Boskirk, E.; Jackson, M. E.
Plate Boundary Observatory Borehole Strainmeter Recordings Of The 29 September 2009 Tsunami
NASA Astrophysics Data System (ADS)
On 29 September 2009 a M8.3 earthquake on the Australian-Pacific plate boundary generated a tsunami that caused widespread damage in Samoa, American Samoa, and Tonga. Peak to trough wave heights of 314 cm were recorded 250 km from the epicenter at Pago-Pago, American Samoa approximately 20 minutes after the event. NOAA's West Coast and Alaska Tsunami Warning Center predicted the tsunami would arrive at Tofino, Vancouver Island, British Columbia, at 05:12 UTC, 30 September 2009. The Plate Boundary Observatory has installed 74 borehole strainmeters along the western United States for the purpose of recording short-term strain transients associated with plate boundary deformation. Two of these strainmeters, Ucluelet and Bamfield, are located on the west coast of Vancouver Island within a few hundred meters of the shore. A third, Port Alberni, is located at the eastern end of Port Alberni Inlet, ~ 50 km inland. The Ucluelet and Bamfield strainmeters recorded signals associated with the arriving tsunami at times consistent with that recorded by tide gauges at Tofino and Bamfield, ~05:45 UTC. A much smaller signal was recorded about 24 minutes later at Port Alberni. The tsunami strain signals were below the detection level of PBO GPS on the Oregon coast and seismometers in the strainmeter boreholes. Strainmeters, or lower coast tiltmeters, could potentially, provide a reliable onshore detection of a tsunami. In this presentation we document the nature and frequency content of the tsunami signal as recorded by PBO strainmeters and compare these strain measurements against the crustal loading signature predicted by water height changes at nearby tide gauges
Hodgkinson, Kathleen; Mencin, David; Borsa, Adrian; Jackson, Mike
Structural Architecture and Evolutionary Plate-Boundary Processes along the San Jacinto Fault Zone
NASA Astrophysics Data System (ADS)
Problems of continental dynamics are typically studied with frameworks that assume smooth continuous processes. Such models provide important insights on large-scale phenomena far from plate boundaries, but they are not useful near the plate boundaries themselves where deformation processes and structures exhibit highly episodic, complex, and ultimately localized patterns in space and time. In such regions small and large scale structural features develop in the brittle crust by the accumulation of slip on seismogenic faults. An understanding of continental dynamics near plate boundaries requires an approach that accounts explicitly for the interplay between earthquakes and fault evolution. Seismic ruptures lead to the modification of the geometry, internal structure and material properties of fault zones. Conversely, the nucleation, growth and arrest of earthquake ruptures, seismic radiation, inter- and post-seismic deformation, and local seismicity patterns are controlled by the fault zone structure. To address these feedback mechanisms it is important to study the coupled evolution of earthquakes and faults. This is done with funding from the CD program of NSF in the context of the San Jacinto fault zone and surrounding environment in southern California. The project includes collection, analyses and joint interpretation of seismic, geodetic and geological data within and around the internal structure of the San Jacinto fault zone. Recent results include detailed tomographic images of fault zone damage, bimaterial interfaces and basins in the fault zone area, earthquake source properties in different fault sections, analysis of geodetic data accounting for the 3D variations of elastic moduli in the tomographic images, detailed geological mapping of rock damage, paleoseismic records at several sites along the fault, and computer simulations of long seismic catalogs that account for the available seismic and geological data. Examples results will be presented in the meeting.
Ben-Zion, Y.
Velocity field across the southern Caribbean plate boundary and estimates of Caribbean\\/South-American plate motion using GPS geodesy 1994-2000
Global Positioning System (GPS) observations between 1994 and 2000 at twenty-two sites in the Lesser Antilles and northern South-America indicate that the Caribbean plate, along its southern boundary, slips at a rate of 20.5+\\/-2mm\\/a with an azimuth of N84�+\\/-2�E at 65�W, relative to the South-American plate. East of 68�W, 80% of the dextral slip is contained within a 80-km wide
Omar J. P�rez; Roger Bilham; Rebecca Bendick; Jos� R. Velandia; Napole�n Hern�ndez; Carlos Moncayo; Melvin Hoyer; Mike Kozuch
Linear stability analysis in compressible, flat-plate boundary-layers
The stability problem of two-dimensional compressible flat-plate boundary layers is handled using the linear stability theory.\\u000a The stability equations obtained from three-dimensional compressible Navier�Stokes equations are solved simultaneously with\\u000a two-dimensional mean flow equations, using an efficient shoot-search technique for adiabatic wall condition. In the analysis,\\u000a a wide range of Mach numbers extending well into the hypersonic range are considered for
Serkan �zgen; Senem Atalayer K?rcal?
Evolution of southern Caribbean plate boundary, vicinity of Trinidad and Tobago
NASA Astrophysics Data System (ADS)
The tectonic evolution of the southeastern corner of the Caribbean is examined, using field data from the El Pilar fault zone of Trinidad and offshore seismic data. It is found that the dominant process in the region's tectonic evolution is strike-slip motion on at least five major fault systems in a 250-km wide east-west-trending plate-boundary zone extending from Grenada in the north to the Orinoco River in the south. The geological effects of this evolution over the past 30 m y are described.
Robertson, Paul; Burke, Kevin
Non-Similarity Thermal Boundary Layer Flow over a Stretching Flat Plate
NASA Astrophysics Data System (ADS)
Steady non-similarity thermal boundary layer flow over a stretching flat plate is investigated. The velocity and temperature on the surface are assumed to vary with the distance. The energy equation is solved with the homotopy analysis method which is suitable for strongly non-linear problems. This approach is more general than the similarity methods and is valid in the whole spatial and temporal regions. The results are compared with the similarity solutions for special cases of velocity and temperature profiles on the wall. The effect of different parameters on the Nusselt number and temperature profiles is investigated.
M. Erfanian, Nakhchi; R. H. Nobari, M.; H. Basirat, Tabrizi
Experimental study of boundary layer transition on a heated flat plate
NASA Technical Reports Server (NTRS)
A detailed investigation to the document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were done in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate, and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for momentum thickness Reynolds number, Re(sub theta) less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length and uniform heat flux. A small dependence of turbulence results on the freestream turbulence intensity was observed.
Sohn, K. H.; Reshotko, E.; Zaman, K. B. M. Q.
Young tectonics of a complex plate boundary zone: Indentation, rotation, and escape in Alaska
NASA Astrophysics Data System (ADS)
Convergence of thick crust of the Yakutat block with the southern margin of Alaska is widely recognized as a dominant influence on the tectonics of Alaska since at least late Miocene time. It is less clear how this convergence relates to the distribution, type, and orientation of geologic structures, and to the boundaries between the tectonic provinces that they define. We propose that convergence of Yakutat block includes two distinct components that influence deformation and topography in different ways: 1) The crust of the exposed, southern Yakutat block is too thick to subduct, which has caused the collisional St. Elias orogen. Detachment of the upper part of the mafic basement allows delamination and sinking of the remaining mafic crust and lithospheric mantle. The collisional orogen drives rigid counterclockwise rotation of the southern Alaska block south of the arcuate, right-lateral Denali fault. The western boundary of this block is a zone of distributed contraction in the western Alaska Range and Cook Inlet. 2) The northern part of the Yakutat block is thin enough to subduct but thick and buoyant enough to cause localized flat-slab subduction orthogonal to rotation of the southern Alaska block. Consequences include the gently antiformal Talkeetna Mountains that span the forearc basin, a gap in the magmatic arc, and a basement-involved fold-and-thrust belt in the northern Alaska Range. An arcuate oroclinal hinge from southern Alaska to the northeastern Brooks Range reflects indentation since at least Paleocene time. Traction above the subducted Yakutat block along the southern part of this hinge drives current indentation. North of the subducted Yakutat block, indentation is reflected by left-lateral block rotation that accommodates shortening between the Denali and Tintina faults and by contraction farther north along the northern edge of the arcuate northeastern Brooks Range. Western Alaska accommodates both northward indentation and westward convergence of the southern Alaska block by right-lateral block rotation and tectonic escape related to local left-lateral faults. Farther west, slow clockwise rigid rotation of the extensive Bering block accommodates escape and is separated from stable northwestern Alaska by a zone of extension. These tectonic provinces are defined by mapped structures and by the distribution and focal mechanisms of earthquakes. Structures are generally consistent with stress orientations determined from earthquakes, but local discrepancies between observed structures and those predicted from the stress determinations suggest that reactivation of older structures is important.
Wallace, W. K.; Ruppert, N. A.
The Relation Between Tectonics, Fluid Flow and Seismogenesis at Convergent Erosional Margins
The integration of seismic reflection images, multibeam bathymetry, sidescan sonar images, seafloor observations, heat flux measurements and well-located microearthquakes show the relationship between tectonics, fluid flow and seismic activity at the erosional Middle America convergent margin. Seismic images show that the plate boundary is characterized by large amplitude reflections under the continental slope. The amplitude of plate-boundary reflectivity rapidly decreases
C. R. Ranero; W. Weinrebe; I. Grevemeyer; R. von Huene; C. Reichert
Using GPS, tide gauge and altimetry data to constrain subduction parameters at the Vanuatu plate boundary.
NASA Astrophysics Data System (ADS)
The Vanuatu subduction zone, Southwest Pacific, combines several features that makes it a particularly useful place to study seismic cycles. The convergence rate is high - approximately 12 cm/yr - and the seismic cycle relatively short. Measurements of interseismic motions are helped by relatively high vertical rates, the close proximity of some islands to the plate interface and the existence of very shallow seamounts on either side of the plate interface. The Vanuatu archipelago is part of the Pacific Ring of Fire: the Australian plate subducts eastward beneath the North Fiji basin, on the western border of the Pacific Plate. High topographic features on the diving plate may contribute to locking of the plates, which can play a major role in the genesis of destructive earthquakes. GPS network points were installed in the early 1990s and the geodesy network has been densified through the years, enabling us to map interseismic horizontal and vertical deformation rates throughout the archipelago. More recently, 8 continuous GPS stations were installed, along with 3 continuous seafloor pressure gauges very near to the plate interface. We show results from GPS data collected from 1996 to 2011, that we re-processed and combined into the ITRF2008 reference frame, and altimetry and seafloor pressure data from 1999 to 2010. The GPS results show that vertical deformation rates vary both across and along the archipelago. We believe that these variations result from variable distance to the plate limit and variable locking parameters. In some areas, subsidence rates are close to one centimeter per year. In the Torres islands (at the northern end of the archipelago) where villagers face recurrent coastal flooding, we showed that this flooding is due more to ground motion than to rise in the absolute sea level, even though the sea-level rise rates are locally high and the islands uplift over the long term. In the Central area of Vanuatu, we augmented the on-land network with two offshore sites using absolute pressure gauges. The sites - Wusi and Sabine Banks - are installed beneath altimetry satellite tracks, Wusi Bank on the over-riding plate and Sabine Bank on the subducting plate. The difference in the pressure records between the sites shows that Wusi Bank subsides by 11 +/- 3 mm/yr with respect to Sabine Bank. We combined the water depths derived from the pressure measurements with altimetry-derived sea-surface heights to tie these heights to a global reference frame: Wusi Bank subsides and Sabine Bank's vertical motion is near zero. Using a 2D elastic model and a finite-element code, we used the gradient of vertical deformation between the coast and the Wusi Bank site to discriminate between possible locked zone geometries. The best simple approximation is a 25� dipping, 30 km long fully locked zone, indicating that stress is currently accumulating west of Santo, Central Vanuatu. The movement of Wusi Bank is a key factor in constraining the dip and length of the locked zone, demonstrating the importance of offshore geodesy measurements.
Ballu, V.; Bouin, M.; Baillard, C.; Calmant, S.; Pelletier, B.; Crawford, W. C.; Kanas, T.; Garaebiti, E.
The memory of the accreting plate boundary and the continuity of fracture zones
A detailed aeromagnetic anomaly map of the Mesozoic seafloor-spreading lineations southwest of Bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation. The magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone (flowline) trends. The linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones. During the period of Mesozoic geomagnetic polarity reversals (when 1200 km of central North Atlantic seafloor formed), the Atlantic accreting boundary consisted of stationary, elongate, spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells. Normal oceanic crustal structure was formed in the spreading center cells, but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries, which parallel flowlines of Mesozoic relative plate motion in the central North Atlantic. We suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest; here, each spreading center cell independently goes through its cylce of stress buildup, stress release, and crustal accretion, after which its memory is refreshed. The temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists. ?? 1982.
Schouten, H.; Klitgord, K. D.
Flowfield measurements in a separated and reattached flat plate turbulent boundary layer
NASA Technical Reports Server (NTRS)
The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.
Patrick, William P.
Low Intensity Characteristic of Plate-Boundary S-S Reflections Within a Region of Strong Plate-Boundary P-P Reflections and low Seismicity Along the Japan Trench Subduction Zone
NASA Astrophysics Data System (ADS)
It has been pointed out that the epicenters of the microearthquakes along the forearc slope of the Japan Trench are not uniformly distributed but clustered in seismically active zones that are oriented perpendicular to the trench axis. One of the clear seismic-aseismic boundaries of such seismic clusters can be identified in latitude 39� N. A seismic survey was conducted in 1996 with one profile running across the boundary and parallel to the trench axis, and a P-wave velocity structure model was obtained by travel-time inversion (Fujie, 1999). A strong anti-correlation between the seismicity and the intensity of the plate-boundary P-P reflected waves was found: strong plate-boundary P-P reflected waves were observed in a region where seismicity is quite low, and vice versa (Fujie et al., 2002). They discussed that a thin layer of low P-wave velocities (3~4 km/s) with its thickness up to a few hundred meters along the plate boundary could explain the intensity of the reflections. Results of finite-difference waveform calculations support this estimation (Moghaddam, 2002). Another seismic survey was carried out in 2001 with 7 trench-parallel profiles in the same region as the 1996 survey in order to map and verify the strong anti-correlation. The strong anti-correlation was observed over the seismic-aseismic boundary region, and it was inferred that a thin layer with low P-wave velocities along the plate boundary exists beneath the aseismic zone in the region. Understanding the characteristics of plate-boundary S-S reflections in addition to those of P-P reflections would greatly help put better constraints on the physical properties along the plate boundary. Substantial P-to-S conversion at the base of the sedimentary layers was observed. S-wave velocities, especially those of the sedimentary layers, should be precisely determined in order to have good estimates of the arrival times of the plate-boundary S-S reflected waves. The S-wave velocities of the sedimentary layers were obtained by the tau-p analysis of the OBS horizontal-component waveforms. The Vp/Vs ratios within the sediment layers were estimated to be 5.2 and 2.3 from top to bottom. The Vp/Vs ratios within the deeper structure were assumed to be 1.8 to 1.74 as the Vp varies from 4.5 km/s to 8.0 km/s. The calculated travel times explain well the observed travel times of P-S-converted refraction arrivals. Expected arrival times of the plate-boundary S-S reflected waves were calculated with respect to the obtained Vs structure. Such intense amplitude as observed for the plate-boundary P-P reflections was not identified for the S-S reflections. Irregularity of the interfaces within the structure or differences in the reflectivity coefficients between P-P and S-S reflections at the plate boundary does not explain the opposite appearances of those reflections. Although the strong plate-boundary P-P reflections could be explained by putting a thin low-velocity layer, some additional features for S-S reflections along the plate boundary may be required, such as very low Q values (high attenuation) for the S-wave propagation.
Mochizuki, K.; Kasahara, J.; Hino, R.; Nishino, M.; Yamada, T.; Shinohara, M.; Kanazawa, T.
Reconstruction convergence and speed enhancement in electrical impedance tomography for domains with known internal boundaries.
An improved approach for electrical impedance tomography (EIT) image reconstruction, based on modifying the forward and inverse solutions, is proposed. In this approach, the EIT forward problem is solved via the finite element method (FEM) using two types of elements. The inverse problem is solved by the modified Newton-Raphson method, whereas the condition number of the Hessian matrix is being monitored. At the early stage of the reconstruction, first-order elements are used, and if the condition number exceeds the allowable limit, the algorithm restarts. Otherwise, if the reconstruction error becomes lower than a predefined threshold, second-order elements are employed in the forward solution in order to preserve the precision of the final results. The latter stage converges in very few iterations. Since the solution speed with the first-order FEM is considerably higher than the second-order FEM, the reconstruction speed improves considerably by this approach, whereas the accuracy of the results is guaranteed by the well-conditioned Hessian matrix. Numerical simulations and experiments are followed by comparisons with other reconstruction methods which demonstrate the reliability and high solution speed of this approach. According to the results, the convergence of the proposed method is significantly improved, and its speed is 2-200 times higher than the previously developed methods with the same level of precision. PMID:20938064
Rezajoo, Saeed; Hossein-Zadeh, Gholam-Ali
What on Earth is Plate Tectonics?
NSDL National Science Digital Library
This web site was put together by the U.S.G.S. (United States Geological Survey) and the N.P.S. (National Park Service) and provides an overview of plate tectonics. It begins by explaining about the Earth's core, mantle, and crust. It then discusses the crustal plates and the types of plate boundaries (convergent, divergent and transform). The lesson ends with paleogeographic reconstructions of plate distributions from the past 650 million years.
Seismicity and seismotectonics of the diffusive Iberian/African plate boundary: Horseshoe Abyssal Plain and Gorringe Bank
NASA Astrophysics Data System (ADS)
In the area to the west of the Gibraltar Arc the plate boundary between Africa and Iberia is poorly defined. The deformation in the area is forced by the slow NW-SE convergence of 4 mm/yr between the oceanic domains of Iberia/Eurasia and Africa and is accommodated over a 200 km broad tectonically-active deformation zone. The region, however, is also characterized by large earthquakes and tsunamis, such as the 1969 Mw=7.9 Horseshoe Abyssal Plain earthquake and the November 1, 1755 Great Lisbon earthquake with an estimated magnitude of Mw~8.5. The exact location of the source of the 1755 Lisbon earthquake is still unknown. Recent work may suggest that the event occurred in the vicinity of the Horseshoe fault, an oblique thrust fault. However, estimates of tsunami arrival times suggested a source near the Gorringe Bank, a ~180 km-long and ~70 km-wide ridge that has a relieve of ~5000 m. Deep Sea Drilling (DSDP) and rock samples indicated that the bank is mainly composed of serpentinized peridotites with gabbroic intrusions, perhaps being created by overthrusting of the Horseshoe Abyssal Plain onto the Tagus Abyssal Plain in NW direction. Further, the Horseshoe Abyssal Plain is marked by the presence of compressive structures with a roughly NE-SW orientation and E-W trending, segmented, crustal-scale, strike slip faults that extend from the Gorringe Bank to the Gibraltar Arc in the eastern Gulf of Cadiz, which were called "South West Iberian Margin" or SWIM faults. The fault system may mark a developing Eurasia-Africa plate boundary. Two local seismic networks were operated in the area. First, a network of 14 ocean-bottom seismometers (OBS) was operated between April and October 2012 in the vicinity of the Horseshoe fault between 10�W to 11�W, and 35�50'N to 36�10'N. From October 2013 to March 2014 a second network of 15 OBS monitored seismicity at the Gorringe Bank. Both networks benefitted from seismic stations operated in Portugal. The first network provided in the order of 100 locale earthquakes occurring with the network. Most earthquakes in the Horseshoe occurred at a depth of 40-60 km, either in oceanic or unroofed continental mantle. The large source depth of events observed in the Horseshoe Abyssal Plain supports the idea that large catastrophic earthquakes, like the Great Lisbon earthquake of 1755, may indeed occur in the area.
Grevemeyer, Ingo; Lange, Dietrich; Matias, Luis
Fluid flow and heat transfer of carbon nanotubes along a flat plate with Navier slip boundary
NASA Astrophysics Data System (ADS)
Homogeneous flow model is used to study the flow and heat transfer of carbon nanotubes (CNTs) along a flat plate subjected to Navier slip and uniform heat flux boundary conditions. This is the first paper on the flow and heat transfer of CNTs along a flat plate. Two types of CNTs, namely, single- and multi-wall CNTs are used with water, kerosene or engine oil as base fluids. The empirical correlations are used for the thermophysical properties of CNTs in terms of the solid volume fraction of CNTs. For the effective thermal conductivity of CNTs, Xue (Phys B Condens Matter 368:302-307,
Khan, W. A.; Khan, Z. H.; Rahi, M.
Relaminarization of the boundary layer over a flat plate in shock tube experiments
NASA Technical Reports Server (NTRS)
The relaminarization of the boundary layer over a flat plate in the shock tube was investigated by using the partially reflected shock wave technique. The flow Mach number was approximately 0.14, which corresponds to the inleft flow Mach number for the first row of vanes in a gas turbine. The thin film platinum heat gauges were used to measure the heat transfer rate and the Stanton number was calculated from the oscilloscope voltage traces. The Reynolds number was varied by changing the operation pressure of the shock tube and the values varied from 2.3 x 10 to the 4th to 5.3 x 10 to the 5th. For a Reynolds number range of 7 x 10 to the 4th to 3.5 x 10 to the 5th, the relaminarization of the boundary layer was observed. This phenomenon is due to the decay of the turbulence level in the flow as the reflected shock wave moves upstream from the flat plate. As the Reynolds number increased, the relaminarization was delayed and the delay was related to the turbulence generated by the reflected shock wave.
Hinckel, J. N.; Nagamatsu, H. T.
Seismic imaging of a plate boundary in the eastern margin of the Japan Sea
NASA Astrophysics Data System (ADS)
Large earthquakes have frequently occurred in the eastern margin of the Japan Sea (e.g., the 1964 Niigata earthquake (MJMA 7.5), 1983 Nihonkai-Chubu earthquake (MJMA 7.7), 1993 Hokkaido-Nansei-Oki earthquake (MJMA 7.8)), and these earthquakes have caused very strong vibrations, large tsunamis, and serious damage on the coast of the Japan Sea. Nakamura (1983) and Kobayashi (1983) suggested that the eastern margin of the Japan Sea is located along the boundary between the Eurasian Plate and the North America plate. However, since this area has not been identified as one of the priority areas to be investigated, the observation didn't obtain exact evidence of a plate boundary in the eastern margin of Japan Sea. Therefore, we have performed seismic surveys at the eastern margin of the Japan Sea since 2009. Objectives of this study are to reveal structural characteristics around a plate boundary of the Japan Sea with the large earthquakes and understand the tectonics as the geologic background. In 2009-2011, we conducted a multi-channel seismic (MCS) survey and ocean bottom seismometer (OBS) survey around the Yamato basin and the eastern margin of the southern Japan Sea using the R/V KAIREI, JAMSTEC (Japan Agency for Marine-Earth Science and Technology). Survey lines were crooked to avoid the many fishing operations and equipment in the survey area. We shot a tuned airgun array with a spacing of 50 m. This array has a total capacity of 7,800 cubic inches (about 130 liters). The standard air pressure was 2,000 psi (about 14 MPa). During the shooting, we towed a 444-channel hydrophone streamer cable with a 5600-m maximum offset, and the group interval was 12.5 m. The towing depth of the streamer cable was maintained at 12 m below the sea surface using depth controllers. The sampling rate was 2 ms, and the recording length was 15 s. We deployed OBSs, and a refraction survey using an airgun array with a spacing of 200 m. An airgun array in OBS survey used the same configuration as MCS survey. The interval of the OBS deployment was about 5 km or 7 km. We present an outline of the data acquisition and preliminary results of data processing and interpretations in this study. As observed from preliminary results, our imaging are suggested that deformation structure has accompanied past large earthquakes such as the rupture zone of the 1964 Niigata earthquake (MJMA 7.5) and the 2007 Niigata-ken Chuetsu-oki earthquake (MJMA 6.8).
No, T.; Sato, T.; Takahashi, N.; Kodaira, S.; Kaneda, Y.
A Three-Dimensional Seismic Model of the Dead Sea Plate Boundary From Active Source Data
NASA Astrophysics Data System (ADS)
The Dead Sea fault system is a north-south striking left-lateral shear zone separating the African and Arabian tectonic plates. The southern part of the plate boundary is located within the Dead Sea valley. The valley, much of it below sea level, is surrounded by highlands on both sides, and contains subsurface sedimentary basins, including the large (~150 km long) a deep (6-8 km) Dead Sea basin. A wide-angle seismic reflection and refraction experiment was carried out in the Dead Sea Region in October 2004 to study the deep structure of the plate boundary. The experiment consisted of two perpendicular profiles a 280-km long profile along the valley and the international border between Jordan, Israel and the Palestinian Territories, and a 250 km long profile from Gaza strip to eastern Jordan across the Dead Sea basin. Modeling of the West-East line shows a low velocity zone extending to a depth of 18 km below the basin, which includes >6 km of "syn-rift" sediments (ten Brink et al., GRL, 2006). The lower crust and Moho are not perturbed. The uplift surrounding the Dead Sea Transform also appears to be an upper crustal phenomenon. The shear deformation, associated with the transform plate boundary motion appears, on the other hand, to cut throughout the entire crust (Ibid.). Two-dimensional modeling of the South-North line is more complex due to the fact that sedimentary basins do not occupy the entire width of the valley hence some sources and some receivers are located within the basins whereas others are located outside. This heterogeneous near-surface structure explains why a simple 2-D velocity model does not fit the observed travel times from all shots. Therefore, we are using 3-D travel-time tomography to model the heterogeneous near-surface and deeper structure of the Dead Sea. Preliminary models indicate that some ray-paths from sources near the basin use the edges of the basin as a wave-guide and generate earlier than expected arrivals at receivers near the shot. We find seismic confirmation of sub-basins along the Dead Sea Transform that have been identified using gravity and aeromagnetic surveying (ten Brink, et al., G-cubed, 2007, ten Brink, et al., Geology, 1999), and will present a preliminary model for variations in the crustal structure.
Flores, C. H.; ten Brink, U. S.
Inter- and Intra-Plate Deformation at North American Plate Boundaries. Semiannual Status Report July 1, 1986-December 31, 1986.
National Technical Information Service (NTIS)
Alaska tectonics and earthquake hazard studies; Southern California tectonics (block rotation); spreading near the Salton Trough; California plate motion (fault zone kinematics); and Caribbean plate motion investigations are examined.
J. Beavan
Large-Eddy Simulation of the Flat-plate Turbulent Boundary Layer at High Reynolds numbers
NASA Astrophysics Data System (ADS)
The near-wall, subgrid-scale (SGS) model [Chung and Pullin, "Large-eddy simulation and wall-modeling of turbulent channel flow'', J. Fluid Mech. 631, 281--309 (2009)] is used to perform large-eddy simulations (LES) of the incompressible developing, smooth-wall, flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. This is then used to study several aspects of zero- and adverse-pressure gradient turbulent boundary layers. First, LES of the zero-pressure gradient turbulent boundary layer are performed at Reynolds numbers Retheta based on the free-stream velocity and the momentum thickness in the range Retheta = 103-1012. Results include the inverse skin friction coefficient, 2/Cf , velocity profiles, the shape factor H, the Karman "constant", and the Coles wake factor as functions of Re theta. Comparisons with some direct numerical simulation (DNS) and experiment are made, including turbulent intensity data from atmospheric-layer measurements at Retheta = O (106). At extremely large Retheta , the empirical Coles-Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot of itself probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that the LES is suggestive of the asymptotic, infinite Reynolds-number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum Retheta of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger Retheta could be achieved with quad- or higher-precision arithmetic. Second, the time series velocity signals obtained from LES within the logarithmic region of the zero-pressure gradient turbulent boundary layer are used in combination with an empirical, predictive inner--outer wall model [Marusic et al., "Predictive model for wall-bounded turbulent flow'', Science 329, 193 (2010)] to calculate the statistics of the fluctuating streamwise velocity in the inner region of the zero-pressure gradient turbulent boundary layer. Results, including spectra and moments up to fourth order, are compared with equivalent predictions using experimental time series, as well as with direct experimental measurements at Reynolds numbers Retau based on the friction velocity and the boundary layer thickness, Retau = 7,300, 13,600 and 19,000. LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers Retau = 62,000, 100,000 and 200,000 that lie within a gap in log(Retau) space between laboratory measurements and surface-layer, atmospheric experiments. The present results support a log-like increase in the near-wall peak of the streamwise turbulence intensities with Retau and also provide a means of extending LES results at large Reynolds numbers to the near-wall region of wall-bounded turbulent flows. Finally, we apply the wall model to LES of a turbulent boundary layer subject to an adverse pressure gradient. Computed statistics are found to be consistent with recent experiments and some Reynolds number similarity is observed over a range of two orders of magnitude.
Inoue, Michio
Late Cretaceous/early Tertiary convergence between the Indian and Arabian plates recorded in ophiolites and related sediments
NASA Astrophysics Data System (ADS)
Remnants of ocean floor forming the Eastern Ophiolite Belt in Oman and the Western Ophiolite Belt in Pakistan have a common plate-tectonic history culminating in emplacement at the Cretaceous/Tertiary boundary. Fragments of ocean floor in these two belts have ages between 150 and 65 Ma and recorded tectonic events in the early Indian Ocean at 150 Ma, 130-120 Ma, 110-100 Ma and 70-65 Ma. New radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving Indian Ocean, which was characterised by the stepwise breakup of Gondwana at 158 Ma (East and West Gondwana), 130 Ma (Southern Atlantic, breakup of East Gondwana), 95-84 Ma (Madagascar and India/Seychelles), 65 Ma (India and Seychelles) and, finally, at 40 Ma, rifting between Africa and Arabia. The 150-Ma-old oceanic rocks of Masirah Island in Oman originally formed the extension of the basins now preserved along the eastern edge of the Afro-Arabian plate. Masirah drifted together with India-Seychelles when a new ridge formed at approximately 130 Ma separating microplates (e.g., Kabul Block) from the northern edge of Greater India. Parts of this new ocean were later emplaced to form the western ophiolite belt in Pakistan. Consumption of oceanic crust and emplacement of ophiolites during the closure of the Neotethys occurred not only north of India (� Seychelles), but also along two or three subduction zones between the Afro-Arabian plate and India/Seychelles, documented by the formation of metamorphic soles beneath ophiolites. Relics of ocean floor formed approximately 65-70 Ma ago, now form the upper units in the Western Ophiolite belt of Pakistan where they overlie an accretionary prism of pillow lavas of dominantly (Aptian-) Albian age and sedimentary rocks. The breakup of India and the Seychelles at 65 Ma was associated with the eruption of flood basalts (Deccan and Seychelles) and enhanced counter-clockwise movement of India. This breakup possibly caused the Late Jurassic/Early Cretaceous fragments of ocean floor (e.g., Masirah) to be thrust onto the eastern edge of Oman. The ophiolites, which were emplaced onto the western edge of India, drifted as part of this plate farther north where collision with Eurasia and the accreted microplates occurred in the Eocene (� 55 Ma).
Gnos, E.; Immenhauser, A.; Peters, Tj.
Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate
NASA Technical Reports Server (NTRS)
A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.
Sohn, Ki-Hyeon; Reshotko, Eli
Tour of Park Geology: Plate Tectonics
NSDL National Science Digital Library
This National Park Service (NPS) site provides links to geology field notes providing information about National Parks, National Monuments, and National Recreation Areas that have to do with plate tectonics. The site also has illustrations and descriptions of different plate boundaries. The parks are divided into categories depending on which type of plate boundary they are located on. This includes divergent boundaries(active and ancient), convergent boundaries (ocean-ocean, continent-continent, continent-ocean), transform faults, hot spots, and accreted terrains. Parks referenced include Virgin Islands National Park, Florissant Fossil Beds National Monument, Hawaii Volcanoes National Park, and many more.
Neogene Basin and Plate Boundary Development in the Outer Continental Borderland Offshore Southern California
NASA Astrophysics Data System (ADS)
Mapping using recently released industry multichannel seismic reflection data suggests that uplift associated with continental rifting has played a major role in the Neogene evolution of the Pacific-North American plate boundary in the Outer California Continental Borderland. Up to 3-4 km of basin subsidence, followed by basin inversion, has also occurred. These events are associated with oblique crustal rifting and translation of this area away from the Peninsular Ranges located to the east, as the current transform plate boundary developed. The lithologies and ages of the horizons mapped in the seismic data were correlated with data from industry exploratory wells and two ODP sites. Bathymetry data were also used to analyze the current seafloor topography. The Nicolas terrane is the inner of two tectonostratigraphic regions that compose the Outer Borderland and represents the forearc basin of the former Farallon-North American subduction zone. Our mapping of the Nicolas terrane extends from San Nicolas Island south to the offshore US-Mexico border, and includes San Nicolas, East and West Cortes, and Velero basins, the intervening highs, and parts of Cortes and Tanner Banks. An unconformity that occurs mostly along the eastern boundary of the Nicolas terrane apparently formed shortly after the widespread deposition of a volcanic sequence of early Miocene age, and cuts down through the pre-Miocene forearc basin strata to acoustic basement. This suggests the boundary is related more to crustal uplift associated with rifting and lower crustal exhumation rather than only to large-scale oblique translation of the Borderland, which has often been previously characterized by either a major strike-slip or normal fault. Faults capable of accommodating large scale strike-slip or other displacement have not been found along much of the heretofore mapped Nicolas terrane boundary. In addition to significant post-uplift basin subsidence, our mapping shows the creation of major fold structures (with anticlines as wide as 50 km and up to 200 km along trend) associated with later basin inversion. A ~3.8 Ma horizon dates the onset of this extensive folding, as well as reverse-fault reactivation, showing that the current basin and ridge topography of the Borderland is relatively young, and not related to earlier tectonic events such as Miocene rifting or ridge subduction. Younger tilted horizons and offset bathymetry suggest that this subsequent folding and faulting has continued through the Quaternary.
de Hoogh, G.; Nicholson, C.; Sorlien, C. C.; Francis, R. D.
Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone
NASA Astrophysics Data System (ADS)
Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during �90 to �87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80�C of cooling on Aruba during 70-60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85-80 Ma and 55-45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at �65 Ma and exhumed rapidly at 55-45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene-early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ?1 km. Late Miocene-recent transpression caused inversion and ?1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.
van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego
Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone
Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80�C of cooling on Aruba during 70�60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85�80 Ma and 55�45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55�45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene�early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ?1 km. Late Miocene�recent transpression caused inversion and ?1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.
van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego
Higher Reynolds Number Measurements on a Flat-Plate Turbulent Boundary Layer in the NDF
NASA Astrophysics Data System (ADS)
The recent two experiments of Osterlund and Hites (e.g., see Osterlund, Johansson and Nagib, Phys. Fluids, vol. 12, no. 9, p. 2360, 2000) are extended to Reynolds numbers based on momentum thickness exceeding 50,000. The present measurements are conducted on a flat plate in zero pressure gradient in the National Diagnostic Facility (NDF). As in our previous work, the wall shear stress is directly measured using oil-film interferometry and hot-wire anemometry is used to measure the velocity. Contrary to the recent conclusions of Barenblatt, Chorin and Prostokishin (Phys. Fluids, vol. 12, no. 9, p. 2159, 2000; and JFM, vol. 410, p. 263, 2000), the mean velocity distribution in the overlap region for these higher Reynolds number boundary layers continues to be very accurately described by the Reynolds-number-independent log law. As concluded by us at this meeting last year and in the recent note by Osterlund et al. (Phys. Fluids, vol. 12, no. 1, p. 1, 2000), the values of the log-law coefficients that best represent the data are ? = 0.38 and B = 4.1. We will also briefly comment on asymptotic analyses of turbulent boundary layer and channel flows with an emphasis on the wall region and the various ways of scaling the boundary-layer outer region.
Nagib, Hassan; Christophorou, Chris; Osterlund, Jens; Monkewitz, Peter
Summary of the stratigraphy and structural elements related to plate convergence of the Quetta-Muslim Bagh-Sibi region, Balochistan, west-central Pakistan
The four major faults that bound the structural terrane are the Frontal (F), Ghazaband-Zhob (GZ), Gwal-Bagh (GB), and Chaman (C) faults. Four major periods of deformation are recognized: (1) emplacement of ophiolitic rocks onto the continental margin of the India plate; (2) convergence of the India-Eurasia plates; (3) deposition of Tertiary-Quaternary molasse units followed by major folding and thrusting, and formation of strike-slip faults; and (4) deposition of Pleistocene molasse units with subsequent folding, thrusting, and strike-slip motion that continues to the present.
Maldonado, Florian; Mengal, Jan M.; Khan, Shahid H.; Warwick, Peter D.
EarthScope Plate Boundary Observatory Data in the College Classroom (Invited)
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3-D strain field across the active boundary zone between the Pacific and North American tectonics plates in the western United States. All PBO data are freely available to scientific and educational communities and have been incorporated into a variety of activities for college and university classrooms. UNAVCO Education and Outreach program staff have worked closely with faculty users, scientific researchers, and facility staff to create materials that are scientifically and technically accurate as well as useful to the classroom user. Availability of processed GPS data is not new to the geoscience community. However, PBO data staff have worked with education staff to deliver data that are readily accessible to educators. The UNAVCO Data for Educators webpage, incorporating an embedded Google Map with PBO GPS locations and providing current GPS time series plots and downloadable data, extends and updates the datasets available to our community. Google Earth allows the visualization GPS data with other types of datasets, e.g. LiDAR, while maintaining the self-contained and easy-to-use interface of UNAVCO�s Jules Verne Voyager map tools, which have multiple sets of geological and geophysical data. Curricular materials provide scaffolds for using EarthScope data in a variety of forms for different learning goals. Simple visualization of earthquake epicenters and locations of volcanoes can be used with velocity vectors to make simple deductions of plate boundary behaviors. Readily available time series plots provide opportunities for additional science skills, and there are web and paper-based support materials for downloading data, manipulating tables, and using plotting programs for processed GPS data. Scientists have provided contextual materials to explore the importance of these data in interpreting the structure and dynamics of the Earth. These data and their scientific context are now incorporated into the Active Earth Display developed by IRIS. Formal and informal evaluations during the past five years have provided useful data for revision and on-line implementation.
Eriksson, S. C.; Olds, S. E.
A mid-Pleistocene deformation transition in the Hula basin: Implications for the tectonic evolution of the Dead Sea Fault plate boundary
NASA Astrophysics Data System (ADS)
The Dead Sea fault (DSF) plate boundary has accommodated relative sinistral motion between the Sinai and Arabian plates since the Neogene. Geologically based models point to a long-term (5-0 ma) N-trending relative motion roughly parallel to the central sector of the DSF. GPS-based calculations of present-day relative motion between the Sinai and Arabian plates indicate a northward increasing convergent component across the DSF, suggesting a kinematic change over the Plio-Pleistocene period. We study the evolving deformation of the Hula rhomb-shaped graben situated along the central sector of the DSF in order to examine the possible kinematic change. The Hula graben is widely accepted as a pull-apart basin, part of a series of basins extending southward. We use a 3-D approach, combining mapped surface structures with subsurface seismic reflection profiles (~173 km) and borehole data (38 boreholes), gathered here into a single geographic information systems database. Results indicate that during the mid-Pleistocene a major tectonic transition modified the structure of the basin fill. A subvertical NNW-trending left-lateral throughgoing strike-slip fault developed diagonally across the basin. Consequently, the basin entered a new geodynamic phase where subsidence was controlled by both the basin bordering faults and the diagonal fault, while the vertical displacement across the transverse faults is minor. Synchronous structural changes recorded in additional localities along the DSF attests to a mid-Pleistocene (~1 ma) regional tectonic transition that was associated with a northward increasing convergent component across the central and northern sectors of the DSF.
Schattner, U.; Weinberger, R.
The giant coastal landslides of Northern Chile: Tectonic and climate interactions on a classic convergent plate margin
NASA Astrophysics Data System (ADS)
Documented for the first time are an extensive suite of late Neogene giant terrestrial coastal landslides along the classic convergent margin of western South America (18� to 24� south). These are remarkable in terms of their unusual abundance and atypical setting, such failures previously being linked with oceanic volcanic edifices or over-steepened glaciated coastlines. Located within the hyper-arid Coastal Cordillera of the Atacama Desert of Northern Chile we report the presence of more than 60 individual large-scale landslides with individual volumes up to 9 km3 developed over a horizontal coastline distance of some 650 km. These landslides were emplaced as a combination of rock avalanches and multiple rotational failures. The majority terminated directly into the Pacific - likely generating significant tsunami hazard to the Chilean and south Peruvian coastline in a region which is today considered to be part of a notorious seismic gap. The proliferation and scale of these Late Neogene giant landslides in this actively uplifting, hyperarid terrain suggests they are the main geomorphic agent for relief reduction, probably triggered by megathrust earthquakes and potentially providing a unique palaeoseismic archive. The temporal and spatial distribution of these giant landslides corresponds with a period of surface steepening of the forearc wedge in the Central Andes and south to north differential uplift associated with factors such as aseismic ridge subduction. The resulting surface gradient increases, combined with the persistent climatic aridity of the region, have served to limit effective relief-reducing geomorphic processes in this oversteepened terrain to large-scale landsliding. The phenomena documented here geospatially link previously recognised large-scale slope failures from the off-shore environment and higher altitude areas of the Andean forearc, suggesting that large-scale landsliding is capable of transferring sediment on a regional scale to the off-shore Peru-Chile trench. This has implications for the friction of the subducting Nazca plate and associated seismicity and uplift.
Mather, Anne E.; Hartley, Adrian J.; Griffiths, James S.
Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone
NASA Technical Reports Server (NTRS)
The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.
Baltuck, M.; Dixon, T. H.
Incorporating rheologic anisotropy in self-consistent models of mantle flow and LPO near plate boundaries
NASA Astrophysics Data System (ADS)
Flow-induced lattice preferred orientation (LPO) in the upper mantle results in detectable seismic anisotropy, which potentially can be used to map out deformation patterns that would illuminate the interplay between lithosphere, asthenosphere, and melting along plate boundaries. An aspect of mineral texturing that warrants additional study is the rheologic consequences of strong fabric such as can develop due to shear near plate boundaries. Are feedbacks due to enhanced stiffness in local regions sufficient to alter the pattern of mantle flow or melting over 100-km scales? Could ease of slip parallel to a foliation plane develop notable decoupling at the base of the lithosphere? We approach the problem using direct estimates of the local effect of LPO on effective viscosity of a mineral aggregate, which is determined as a tensor that may be anisotropic. This updated viscosity will be employed in subsequent flow and temperature field iterations. Based on our prior experience for flow in the vicinity of an oceanic spreading center, a number of factors can impact the flow solution when anisotropic viscosity is incorporated. Therefore, we carefully tested the effect of several model parameters as we began calculations using the ISAIAH FEM code: boundary conditions, discretization near the base of the lithosphere, viscosities across the lithosphere/asthenosphere boundary, the increment specified for an aggregate to move along its flowpath. Results for these preliminary (isotropic) cases show that robust viscosity tensor calculations can be obtained on meshes where robust flow and temperature fields are solved in a time sufficiently short that the next stage will be computationally viable. The next stage will require tracking aggregates along flowpaths for each iteration, computing the viscosity tensors for the evolved LPO of (Eulerian) model elements, and updating the state variable accordingly. For this presentation, we expect to have results for at least a few intermediate coupling cases, where anisotropic viscosity has been incorporated directly in subsequent ISAIAH flow calculations. These will illustrate the types of impact that LPO-related rheologic anisotropy can have on overall mantle flow pattern and any associated modification to the predicted seismic anisotropy.
Blackman, D. K.; Boyce, D.; Dawson, P.; Castelnau, O.
Finite Difference Method for the Acoustic Radiation of an Elastic Plate Excited by a Turbulent Boundary Layer: A Spectral Domain Solution
A finite difference method is developed to study, on a two-dimensional model, the acoustic pressure radiated when a thin elastic\\u000a plate, clamped at its boundaries, is excited by a turbulent boundary layer.\\u000a \\u000a Consider a homogeneous thin elastic plate clamped at its boundaries and extended to infinity by a plane, perfectly rigid,\\u000a baffle. This plate closes a rectangular cavity. Both the
Daniel Mazzoni; Ulf Kristiansen
Crustal structure of the South American�Caribbean plate boundary at 67�W from controlled source seismic data
We present the results of new seismic reflection and wide-angle data across the SE Caribbean plate boundary. The 550 km long N�S profile crosses the structures involved in the active 55 Ma long continent-arc oblique collision between the Caribbean (CAR) and the South American (SA) plate. From the north to the south these structures include the accretionary prism, the extinct
Maria Beatrice Magnani; Colin A. Zelt; Alan Levander; Michael Schmitz
The Australia-Pacific boundary and Cenozoic plate motions in the SW Pacific: Some constraints from Geosat data
Finite poles of Australia-Pacific rotation are calculated using a three-plate (Australia-Antarctica-Pacific) model and published Geosat data analyses of the Indian and Pacific Oceans (GEOS-3P solution). Features identified on maps of Geosat data from SW of New Zealand are used to determine a new best fit finite pole for the prerift (mid Eocene; ~45 Ma) configuration of the Australia-Pacific plate boundary
Rupert Sutherland
Plate boundary reorganization at a large-offset, rapidly propagating rift
NASA Astrophysics Data System (ADS)
THE existence of rapidly spinning microplates along the southern East Pacific Rise has been documented by geophysical swath-mapping surveys1-6, and their evolution has been successfully described by an edge-driven kinematic model7. But the mechanism by which such microplates originate remains unknown. Proposed mechanisms1-10 have generally involved rift propagation11, possibly driven by hotspots or changes in direction of sea-floor spreading. Here we present geophysical data collected over the Earth's fastest spreading centre, the Pacific-Nazca ridge between the Easter and Juan Fernandez microplates (Fig. 1), which reveal a large-offset propagating rift presently reorganizing the plate boundary geometry. A recent episode of rapid 'duelling' propagation of the historically failing spreading centre in this system has created a 120 � 120 km overlap zone between dual active spreading centres, which may be the initial stage of formation of a new microplate.
Hey, R. N.; Johnson, P. D.; Martinez, F.; Korenaga, J.; Somers, M. L.; Huggett, Q. J.; Lebas, T. P.; Rusby, R. I.; Naar, D. F.
Navier-Stokes simulations of the effects of suction holes on a flat plate boundary layer
NASA Technical Reports Server (NTRS)
Direct numerical simulations (DNS) of the Navier-Stokes equations are employed to explore the effects of suction holes on transition in a laminar flat plate boundary layer. The Navier-Stokes equations are cast in vorticity-velocity form. Periodicity is imposed in spanwise direction; all other spatial derivatives are discretized with fourth order compact differences. An explicit fourth order Runge-Kutta scheme is employed for the time-integration of the vorticity transport equations. Suction is applied through a row of holes aligned in spanwise direction. For low suction strengths, each hole generates a pair of stable streamwise vortices. When the suction strength exceeds a critical value, the vortices become unstable. For high suction strengths, vortex shedding occurs right at the suction holes. Our numerical findings agree well with experimental observations.
Meitz, Hubert L.; Fasel, Hermann F.
Mantle Tectonics of a Plate Boundary: the North Island of New Zealand
NASA Astrophysics Data System (ADS)
We constrain the extent of lithospheric and asthenospheric deformation by measuring and modelling anisotropy in the North Island of New Zealand through shear wave splitting of teleseismic waves, petrophysical analysis of mantle xenoliths and finite-element modelling of the mantle deformation in a back-arc spreading environment. We use seismic data collected on the GeoNet broadband stations deployed between 2001 and 2004 and a portable deployment in the Northland region. The results for the eastern part of the North Island confirm the earlier pattern. The fast directions are roughly NE/SW, which is parallel to the strike of the Hikurangi subduction zone. In the north of the North Island, two stations present back-azimuthal dependence of the splitting parameters. This dependence suggests a broader and more complex anisotropic effect, such as a dipping axis of symmetry or multiple layers, might be present beneath New Zealand, influencing the measurements on a regional scale. Results from the Northland deployment suggest that splitting from SKS phases decreases as the effects of present plate boundary deformation weaken and allow us to quantify the extent of the plate boundary deformation zone. The petrophysical analysis of mantle xenoliths from the Raglan (North Island) region allows us to constrain the lithospheric contribution to the observed seismic anisotropy. The spinel lherzolites analysed represent mantle material from depths shallower than 75 km and temperatures in excess of 1000�C up to 1150�C. Their extraction ages are less than 2 Myr. The maximum intrinsic anisotropy on the S-wave measured, 3.5%, seems too low to explain the delay times. This indicates that asthenospheric deformation plays the major role there. Through modelling of the lithospheric deformation, derived from surface deformation rates, in the North Island transtensive Central Volcanic Region, we will compare the anisotropy values obtained from the xenoliths to the modelled regional values derived from geodetic movement rates.
Duclos, M.; Savage, M. K.; Tommasi, A.; Gledhill, K. R.
The Formation of the Betic-Alboran System in the Iberia-Africa Plate Boundary: a New Kinematic Evolution Model
NASA Astrophysics Data System (ADS)
Several geodynamic models have been proposed so far to explain the origin and evolution of the Betic-Rif arcuate orogeny and the inner Alboran back-arc basin. Many of these models propose that the Alboran domain underwent a large westward drifting (> 600 km) driven by a subduction rollback, eventually resulting in a symmetric configuration in both the S-Iberia and N-African margins. Alternative models with a more autochthonous component assume that the Oligocene subduction trench extended continuously along the whole Iberian Mediterranean margin from the present Gibraltar arc to the Alps. Common assumptions to all these models are: i) the initial time is about 35 Ma (Eocene-Oligocene), ii) the plate boundary is continuous and non-segmented, iii) the initial subduction polarity is NW-dipping, and iv) the slab must underwent a twisted roll-back to explain the present position of the HP-LT metamorphic rocks involving slab rupture, detachment and tearing. Recent geophysical models based on seismic data, tomography and potential fields draw an arcuate mantle slab restricted below the Betic-Rif orogen, dipping towards the E below the Gibraltar Strait and turning to the SE and S beneath the Betics. In addition, the crust beneath the northern Moroccan margin shows a smooth thinning toward the Alboran basin whereas the southern Iberian margin presents a much sharper thinning. These findings put severe limitations to some of the proposed models and open room for new kinematic proposals. One of the most recent models is based on the following considerations: i) the reconstruction starts in Late Cretaceous times at the onset of northern Africa convergence, ii) displacements and initial configuration are based on plate reconstructions of the Atlantic-Ligurian-Tethys region, and iii) the model assumes that subduction polarity changes laterally from NW-dipping in the Algerian segment to SE-dipping in the Betic-Rif segment. Apart from its simplicity, this model requires a moderate NW to W drifting of the HP-LT metamorphic complexes formed by limited subduction and exhumation, fulfills the imaged crustal and mantle asymmetries, and is compatible with the main geological structures in the region. Cartoon showing the evolution of the Betic-Alboran-Rif system at 9 Ma.
Fernandez, M.; Verges, J.
Complex Faulting in the Pacific-North America Transform Offshore Southern California And Implications on Plate Boundary Tectonics and Tsunamigenesis
NASA Astrophysics Data System (ADS)
Complexity in the tectonic model for Pacific-North America transform motion in the offshore southern California region is demonstrated by earthquakes near San Clemente Island and Fortymile Bank. Observed focal mechanisms show movements opposite to those predicted by the plate tectonic theory for right-slip on NW- trending transform faults and observed in other parts of the California Continental Borderland. Also, there is evidence suggesting that moderate earthquakes in the Inner Borderland have greater magnitudes based on long-period seismic waves than the nominal Richter local magnitudes reported in earthquake catalogs. With better data showing the geologic structure of the area now available, we can try to derive a more complete understanding of this complex tectonic behavior and resulting consequences for local tsunamigenesis. The "backwards" earthquakes suggest the occurrence of plate boundary deformation and/or microplate tectonics with the western side of a block containing Fortymile Bank moving instantaneously faster to the northwest than the adjacent block to the west. Such motions may be consistent with clockwise rotation of blocks in the continental borderland due to the regional dextral shear couple as proposed by Crouch (1978) and Luyendyk and others (1980) based upon paleomagnetic and other geologic data. Alternatively, as initially observed for the 1986 Offshore Oceanside earthquake (MS=5.8) by Hauksson and Jones (1988), the anomalous focal mechanism may be due to an inaccurate model of crustal seismic velocity structure for the offshore region. Use of a refined velocity model may show these anomalous earthquakes to have oblique-reverse mechanisms like the 1986 mainshock. Furthermore, more recent seismicity, located with greater accuracy due to expansion of the Southern California Seismograph Network (SCSN), has apparent NE alignments suggestive of significant active secondary fault structure located off the major NW-trending right-slip faults. Such faulting was also inferred to be significant during the clockwise vertical-axis block rotations of the western Transverse Ranges. Interaction between faults within conjugate systems may enhance vertical movements including subsidence at basins where blocks diverge and uplift where blocks converge, thereby producing local tsunamis during large earthquakes. It was not until recently that local earthquake sources were identified offshore Southern California as potentially damaging tsunami sources. Erroneous magnitude estimate of offshore earthquakes can have serious implications for tsunamigenesis and tsunami warning. A half magnitude error can make the difference between a non-tsunamigenic and a tsunamigenic event especially when a marginal event is considered. Better magnitude estimates using long-period seismographs may be necessary for more accurate identification of potentially tsunamigenic local earthquakes.
Legg, M. R.; Barberopoulou, A.
Implications of the Baja California Microplate Motion on the Deformation Within the Western North America Plate Boundary Zone
NASA Astrophysics Data System (ADS)
Geodetic analysis have shown that the Baja California microplate is moving at ~10% slower rate but in the same direction as the Pacific plate, with respect to North America. Maintenance of the shear zone between Pacific plate and Baja California may be due to the collision of Baja California with the North American plate in the region of the Transverse Ranges in southern California. This restraining bend was created about 16-12 Ma when the North America - Pacific plate boundary jumped inland Baja California, connecting the strike-slip faults of the San Andreas Fault Zone in the north to the transtensional faults along the Gulf of California in the south. The implications of the restraining bend and the Baja California microplate motion onto North America is thought to be responsible for broad deformation along this plate boundary. We study the interaction between the Baja California microplate and the Western North America, in particular the role of inherited geologic structures on strain localization along the Eastern California Shear Zone, south of the Garlock fault. The inherited structures we study include normal faults in the Basin and Range area that become reactivated as strike slip faults, and the Sierra Nevada microplate. We use the numerical modelling technique of finite elements applying the code G- Tecton. All models are 2D spherical caps driven by displacement/velocity boundary conditions calculated from our GPS analysis of rigid plate rotations in the study area.
Plattner, C.; Malservisi, R.; Govers, R.
Prediction and measurement of heat transfer rates for the shock-induced unsteady laminar boundary layer on a flat plate
NASA Technical Reports Server (NTRS)
The unsteady laminar boundary layer induced by the flow-initiating shock wave passing over a flat plate mounted in a shock tube was theoretically and experimentally studied in terms of heat transfer rates to the plate for shock speeds ranging from 1.695 to 7.34 km/sec. The theory presented by Cook and Chapman for the shock-induced unsteady boundary layer on a plate is reviewed with emphasis on unsteady heat transfer. A method of measuring time-dependent heat-transfer rates using thin-film heat-flux gages and an associated data reduction technique are outlined in detail. Particular consideration is given to heat-flux measurement in short-duration ionized shocktube flows. Experimental unsteady plate heat transfer rates obtained in both air and nitrogen using thin-film heat-flux gages generally agree well with theoretical predictions. The experimental results indicate that the theory continues to predict the unsteady boundary layer behavior after the shock wave leaves the trailing edge of the plate even though the theory is strictly applicable only for the time interval in which the shock remains on the plate.
Cook, W. J.
Shear and Normal Strain Effects of Core Layers in Vibration of Square Sandwich Plates Under Clamped Boundary Conditions
NASA Astrophysics Data System (ADS)
The authors previously investigated the effects of both shear and normal strains in the viscoelastic core layer on modal properties of sandwich plates under hinged boundary conditions. For such boundary conditions, analytic formulation of characteristic equations was possible. Agreeing that most real boundary conditions must lie somewhere between hinged and clamped, it is naturally worthwhile to solve for the clamped boundary conditions, for which, however, analytic formulation of the characteristic equations is not possible. In this study, hence, the finite difference method is utilized as a tool for numerical analysis. The effects of neglecting the extensional or compressional strain in the core material for the clamped boundary conditions are studied and compared with the case of simply supported boundary conditions.
Similarity solution for a power-law injection distribution in a flat-plate thermal boundary layer
A similarity solution for the compressible boundary layer on a flat plate cooled by transpiration is derived and discussed. The two-dimensional thermal boundary layer flow is described by the energy equation, the x-momentum equation, and the mass-flow continuity equation. The Prandtl number is assumed to be 1; Sutherland's law is modified to be proportional relation between the dynamic viscosity and
Robert E. Gray
TECHNICAL NOTE: Active vibration control of a plate-like structure with discontinuous boundary conditions
NASA Astrophysics Data System (ADS)
This research involves the application of methods to actively control the vibration of a plate-like structure with discontinuous boundary conditions. The research is motivated by the need to control vibrations on rack shelves in use on the International Space Station (ISS). Vibration of the rack shelves can adversely affect experiments being performed on those shelves. In this work, control of a rack shelf similar to those in use on the ISS is examined. Piezoelectric actuators bonded to the shelf structure are proposed as a method for controlling rack shelf vibrations. A two-dimensional asymmetric piezoelectric actuator model is first developed. The Ritz expansion method is then employed to derive the equations of motion for the combined piezoelectric actuators and rack shelf system with discontinuous boundary conditions. Model parameters from the analytical solution are used in conjunction with experimentally obtained parameters to develop a control model for the active structure. The control model is then used, together with a linear quadratic approach, to develop two different control strategies: collocated output feedback control and modal control. Results from an experimental evaluation of the two control approaches are presented. Based on the experimental results, the two control strategies are shown to be effective in controlling the first several modes of the rack shelf system at frequencies below 800 Hz. Portions of this work were presented in 'Active Control of International Space Station Experiment Rack Shelf Simulator Vibrations', Proceedings of 2004 ASME International Mechanical Engineering Congress, Anaheim, California, November 2004 (IMECE2004-60853).
Wang, Jingdou; Shepard, W. Steve, Jr.; Williams, Keith A.; Gattis, Christy B.
Active faulting in northern Chile: ramp stacking and lateral decoupling along a subduction plate boundary?
NASA Astrophysics Data System (ADS)
Two large features parallel to the coastline of northern Chile have long been suspected to be the sites of young or active deformation: (1) The 700-km long Coastal Scarp, with average height (above sea level) of about 1000 m; (2) The Atacama Fault zone, that stretches linearly for about 1100 km at an average distance of 30-50 km from the coastline. New field observations combined with extensive analysis of aerial photographs demonstrate that both the Coastal Scarp and the Atacama Fault are zones of Quaternary and current fault activity. Little-degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes ( M = 7-8). Normal fault offsets observed in marine terraces in the Coastal Scarp (at Mejillones Peninsula) require tectonic extension roughly orthogonal to the compressional plate boundary. Strike-slip offsets of drainage observed along the Salar del Carmen and Cerro Moreno faults (Atacama Fault system) imply left-lateral displacements nearly parallel to the plate boundary. The left-lateral movement observed along the Atacama Fault zone may be a local consequence of E-W extension along the Coastal Scarp. But if also found everywhere along strike, left-lateral decoupling along the Atacama Fault zone would be in contradiction with the right lateral component of Nazca-South America motion predicted by models of present plate kinematics. Clockwise rotation with left-lateral slicing of the Andean orogen south of the Arica bend is one way to resolve this contradiction. The Coastal Scarp and the Atacama Fault zone are the most prominent features with clear traces of activity within the leading edge of continental South America. The great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth. We interpret the Coastal Scarp to be a west-dipping normal fault or flexure and propose that it is located over an east-dipping ramp stack at the subduction interface. The similar flexure at the western edge of the Altiplano may have the same origin. Ramp stacking along the subduction zone, a mechanism disregarded so far, may be an important thickening process in the Andes and perhaps the basic cause of the uplift of the Altiplano.
Armijo, Rolando; Thiele, Ricardo
Monitoring dynamics of an active plate boundary: Peceneaga-Camena Fault
NASA Astrophysics Data System (ADS)
Peceneaga-Camena Fault (PCF) is one of the well-known regional faults on the Romanian territory, separating the Central Dobrogea from the North Dobrogea structures. Despite its first mentioning more than hundred years ago, some aspects related to its track, nature and dynamics are still debated. After the first geological models assuming it as a reverse fault, or the overthrust plan along which the Upper Proterozoic Green Schist series of Central Dobrogea overthrusted the North Dobrogea Paleozoic structures, PCF started to be considered more as a strike-slip fault. First geophysical evidence (the international DSS line Calarasi-Galati) revealed a 10 km step along it at the both Conrad and Moho levels, thus advocating for its trans-crustal feature. Later on, the re-interpretation of the data provided by Calixto experiment clearly showed in depth extension of the contact down to more than 150 km. This way it becomes clear the lithospheric nature of PCF, as a plate boundary between Moesian Microplate and East European Plate. Concerning the PCF nature and dynamics, several authors have been previously considered the fault as an active trans-current contact along which its southern flank would be pushed towards NW, thus generating the recent Pleistocene folds in the SE bending zone of East Carpathians. The Baspunar experiment was designed and accomplished in order to bring direct evidence on the active character of the PCF. Geomagnetic investigations conducted under the umbrella of a joint project between the Institute of Geodynamics of the Romanian Academy and the Institute of Geophysics of the Ukrainian Academy of Sciences have revealed the presence of an additional local geomagnetic field, due to the inductive currents circulating along the fault plane, which associates well with its assumed active character. A geodetic experiment, during which two Leica TC &TCR total stations were installed and monitored the distance between the PCF flanks, has brought direct evidence on the active nature of the fault, mainly behaving as a right-lateral trans-current plate boundary, in full agreement with previous geodynamic models based on indirect geological evidence.
Besutiu, Lucian; Zlagnean, Luminita
An eddy-viscosity treatment of the unsteady turbulent boundary layer on a flat plate in an expansion tube
NASA Technical Reports Server (NTRS)
An analysis is presented for the relaxation of a turbulent boundary layer on a semiinfinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion tube flows. The flow-governing equations have been transformed into the Lamcrocco variables. The numerical results indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin-friction than a fully laminar boundary layer.
Gupta, R. N.; Trimpi, R. L.
Explicit local buckling analysis of stiffened composite plates accounting for periodic boundary conditions and stiffener�plate interaction
The present contribution is devoted to the closed-form analysis of orthotropic plates under uniaxial uniform compressive load. The plates under consideration are stiffened by open-profile stiffeners in the longitudinal direction which represents a structural situation that is typical, e.g. for many aircraft parts such as tailplanes, wing covers or, at least in an approximate sense, fuselage sections. The analysis method
Christian Mittelstedt
On the use of feedback to control sound radiation from a plate excited by a turbulent boundary layer
It is shown that the problem of applying active control to simply supported plate excited by a turbulent boundary layer can be presented in a form which allows the application of optimal control theory. Linear regulator theory and stochastic linear regulator theory are briefly summarized and the application of the latter to sound radiation from a vibrating structure is illustrated
D. R. Thomas; P. A. Nelson
Transient Strain During and Between Northern Cascadia Episodic Tremor and Slip Events From Plate Boundary Observatory Borehole Strainmeters
Plate Boundary Observatory (PBO) borehole strainmeters provide unique information about the Episodic Tremor and Slip (ETS) events that have recurred every 12-16 months in the reach of the Cascadia subduction zone from south Puget Sound to northern Vancouver Island. PBO strainmeters at seven locations have now recorded the ETS events in January, 2007 and May, 2008 that propagated the entire
E. A. Roeloffs; P. G. Silver; W. A. McCausland
Active crustal fragmentation along the Scotia�Antarctic plate boundary east of the South Orkney Microcontinent (Antarctica)
The structure of the Scotia�Antarctic plate boundary is poorly known east of the South Orkney Microcontinent. New multichannel seismic profiles, together with magnetic, gravity and swath bathymetry data obtained during the SCAN97 cruise, show a complex relief of raised blocks and elongated depressions that may reach more than 6000 m in depth. These depressions develop in relation with extensional active
J. Galindo-Zald??var; J. C. Balany�; F. Bohoyo; A. Jabaloy; A. Maldonado; J. M. Mart??nez-Mart??nez; J. Rodr??guez-Fern�ndez
Pore pressure development beneath the d�collement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering
Despite its importance for plate boundary fault processes, quantitative constraints on pore pressure are rare, especially within fault zones. Here, we combine laboratory permeability measurements from core samples with a model of loading and pore pressure diffusion to investigate pore fluid pressure evolution within underthrust sediment at the Nankai subduction zone. Independent estimates of pore pressure to ?20 km from
Robert M. Skarbek; Demian M. Saffer
Reduction of skin-friction in a microbubble-laden spatially developing turbulent boundary layer over a flat plate
Experimental evidence during the past three decades indicates that injection of gaseous microbubbles into a liquid turbulent boundary layer over a flat plate or over axisymmetrical bodies can reduce the skin-friction by as much as 80% from its value without bubble injection. However, the basic physical mechanisms responsible for that reduction are not yet fully understood. The present study is
Antonino Ferrante
Plate Tectonics Learning Module
NSDL National Science Digital Library
This plate tectonics unit was designed to be used with a college course in physical geography. Subject matter covered includes: the development of the theory including Wegener's Continental Drift Hypothesis and the existence of Pangaea, Harry Hess and his work on sea-floor spreading, and the final theory. It points out that global features such as deep oceanic trenches, mid-ocean ridges, volcanic activity, and the location of earthquake epicenters can now be related to the story of plate tectonics, since most geological activity occurs along plate boundaries. Divergent, convergent and transform plate boundaries are discussed in detail. This module contains a study guide and outline notes, study questions, and practice quizzes. One feature of the module is a web exploration section with links to twelve outside sites that augment the instruction.
Haberlin, Rita
Similarity solution for a power-law injection distribution in a flat-plate thermal boundary layer
NASA Astrophysics Data System (ADS)
A similarity solution for the compressible boundary layer on a flat plate cooled by transpiration is derived and discussed. The two-dimensional thermal boundary layer flow is described by the energy equation, the x-momentum equation, and the mass-flow continuity equation. The Prandtl number is assumed to be 1; Sutherland's law is modified to be proportional relation between the dynamic viscosity and the absolute temperature. Additional assumptions require that the enthalpy difference between fluid in the free stream and that at the wall be large in comparison with the free-stream velocity head, and that the fluid satisfy the perfect equation of state. A solution for an injected flat-plate boundary layer is given. The stream function is discussed and interpreted in the light of calculated values of the convective heat transfer coefficient, and the film effectiveness coefficient.
Gray, Robert E.
Coexisting shortening and extension along the "Africa-Eurasia" plate boundary in southern Italy
NASA Astrophysics Data System (ADS)
We performed geodetic strain rate field analyses along the "Africa (Sicily microplate)"-"Eurasia (Tyrrhenian microplate)" plate boundary in Sicily (southern Italy), using new GPS velocities from a data set spanning maximum ten years (1998-2007). Data from GPS permanent stations maintained from different institutions and the recent RING network, settled in Italy in the last five years by the Istituto Nazionale di Geofisica e Vulcanologia, were included into the analysis. Two dimensional strain and rotation rate fields were estimated by the distance weighted approach on a regularly spaced grid (30*30km), estimating the strain using all stations, but data from each station are weighted by their distance from the grid node by a constant a=70km that specifies how the effect of a station decays with distance from the node grid interpolation. Results show that most of the shortening of the Africa-Eurasia relative motion is distributed in the northwestern side offshore Sicily, whereas the extension becomes comparable with shortening on the western border of the Capo d'Orlando basin, and grater in the northeastern side, offshore Sicily, as directly provided by GPS velocities which show a larger E-ward component of sites located in Calabria with respect to those located either in northern Sicily or in the Ustica-Aeolian islands. Moreover, where shortening and extension have mostly a similar order of magnitude, two rotation rate fields can be detected, CCW in the northwestern side of Sicily, and CW in the northeastern one respectively. Also, 2-D dilatation field records a similar pattern, with negative values (shortening) in the northwestern area of Sicily close to the Ustica island, and positive values (extension) in the northeastern and southeastern ones, respectively. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection profiles acquired in the southern Tyrrhenian seismogenic belt show active extensional faults affecting Pleistocene strata and deforming the seafloor in the western sector of the Cefal� Basin, on both NE-SW and W-E trending faults. Combining geodetic data and geological features contributes to the knowledge of the active deformation along the Africa-Eurasia plate boundary, suggesting coexisting, independent geodynamic processes, i.e., active E-W backarc spreading in the hangingwall of the Apennines subduction zone, and shortening of the southern margin of the Tyrrhenian backarc basin operated by the "Africa" NW-motion relative to "Europe".
Cuffaro, M.; Riguzzi, F.; Scrocca, D.; Doglioni, C.
Lithospheric evolution of the Pacific-North American Plate Boundary considered in three dimensions
NASA Astrophysics Data System (ADS)
Tomographic images developed using the combined seismic networks of California and Nevada provide a three-dimensional view into Neogene Pacific-North American plate boundary evolution. Images reveal structures similar in size and spatial distribution to the large-scale structures observed at the surface. A prominent linear anomaly in the mantle is imaged beneath the western foothills to a depth of 70-90 km. Called the Sierran Foothill Anomaly (SFA), this 1-2% high-velocity structure extends the length of the physiographic Sierra Nevada Mountains. Much of the velocity increase is thermal in origin, with a first episode of cooling during the same late-Cretaceous to Paleogene low-angle subduction that affected most of western North America. Post-Laramide resumption of subduction continued chilling the western SFA. Small thrust earthquakes at the contact between the Juan de Fuca slab and the SFA indicate that the contact is still relatively cold to depths approaching 90 km. We propose that this chilled lithospheric section as responsible for the block-like integrity of the core of the Sierra Nevada. The Peninsular Ranges in southern California have also maintained a high degree of integrity, at least until recent times, because they shared a similar batholithic generation and Laramide chilling as the Sierra Nevada. The tomographic image includes other large-scale features. West of the SFA is a low-velocity region interpreted as upwelling mantle filling the window behind the NW-translating Juan de Fuca slab. This low-velocity feature appears to be offset by the San Andreas fault, which would indicate transform relations extend into the mantle. Compression and shortening between the Peninsular Ranges and the Sierra Nevada blocks began when the transform boundary shifted east of the Peninsular Ranges and Baja California around 5.5 Ma. High-velocity structures in the upper mantle developed beneath the Transverse Ranges and the Southern Great Valley (SGV) to accommodate crustal shortening. Alternative explanations for the SGV Anomaly are explored by comparing the volume of proximal sources to the volume of the sinking SGV Anomaly. No local source such as convective overturning of Sierran block eclogitic roots seems adequate to provide the volume needed to explain the anomaly as a purely local feature. Surface and subsurface views of the plate margin are complimentary, but consistent, and each contributes to resolving problems not accessible to the other.
Biasi, Glenn P.
Analysis of and results from the GPS component of the Plate Boundary Observatory
NASA Astrophysics Data System (ADS)
The first GPS station installed by the Plate Boundary Observatory (PBO) component of the National Science Foundation (NSF) Earthscope program was installed and started operation in January 2004. Since then over 1100 new GPS stations have been installed and combined with over 300 pre-existing GPS stations to form PBO. Analysis of the data from this network is performed daily, with one-day latency, using rapid orbit products from the International GNSS Service (IGS) and weekly, with ~2 week latency, using the final IGS product. A supplemental analysis is also preformed with 12-week latency to add to the final solution data from sites that were not available when the first finals were run. The median weighted root-mean-square (WRMS) scatters of the position results from the combined analyses of these data performed by two different GPS analysis programs, GAMIT at New Mexico Tech and GIPSY at Central Washington University and combined with GLOBK at MIT, are less than 1 mm in North and East (NE) and 3 mm for vertical (U) over monthly durations. The WRMS scatters of the position residuals about linear trends, with offsets for earthquakes and antenna changes removed, from all results processed thus far, ~8 years of data for longest running sites, are ~1.5 mm NE and 4.5 mm U. The top 10% of sites have short period scatters (month duration) of 0.5 mm NE and 1.9 mm U, while the long-term scatters increase to 0.8 mm in NE and 3.3 mm U. The largest RMS sites are generally in volcanic areas and/or affected by snow and ice on the antennas. All of the data from PBO and from an additional 600 GPS sites are being re-processed with data back to 1996 being included in the reprocessing. In this paper, we will present results from this re-processing in terms of secular rates across the Pacific/North America plate boundary and non-secular signals arising from earthquakes (co- and post-seismic deformation) and other natural and human-induced processes.
Herring, T.; King, R. W.; Floyd, M. A.; Murray, M. H.; Melbourne, T. I.; Santillan, V. M.; Mattioli, G. S.; Phillips, D. A.; Puskas, C. M.
The August and October, 2008 earthquake swarms on the Explorer/Pacific plate boundary
NASA Astrophysics Data System (ADS)
In August and October of 2008, earthquake swarms occurred on the Explorer/Pacific plate boundary. The August swarm lasted for approximately 4 days. Seventy-five earthquakes were reported by the Canadian National Seismograph Nework (CNSN), with the largest having a magnitude of 5.9. The U.S. Navy's Sound Surveillance System (SOSUS) hydrophones reported 148 earthquakes. Over 250 earthquakes were recorded on the Central Oregon Locked Zone Array (COLZA), a temporary array of 15 ocean bottom seismometers (OBS) and hydrophones. The October swarm lasted about 2 days with only one reported CNSN magnitude 4.4 earthquake. This event was also observed with the COLZA network. SOSUS reported 119 earthquakes over the course of two days. In this poster, we use the COLZA T-phase data to better understand the tectonic significance of these swarms. T-phases are generated by earthquakes and converted to acoustic energy at the seafloor. We used the ANSS magnitudes to calibrate an empirical magnitude scale for maximum amplitudes handpicked from the COLZA T-phase observations. This enabled us to lower the magnitude threshold to 2.8. A b-value of 0.78 was obtained for the August swarm suggesting that it may be a tectonic event rather then a magmatic one. Focal mechanisms reported by the Harvard CMT catalog for 3 of the largest events also support strike-slip motion. The reported SOSUS hypocenter locations indicate a linear NE/SW trend west of and parallel to the Explorer Ridge while the ANSS locations are very scattered but suggest a northwest/southeast trend in line with but east of the Dellwood-Revere transform fault. To obtain better-constrained locations, we plan to relocate the events and COLZA T-phase data using cross-correlation techniques developed to locate seismic tremor. We expect the COLZA data will allow us to determine whether activity was primarily focused along the Explorer Ridge axis, along the Dellwood-Revere transform, or within the plate. This investigation could provide us with new insight into the evolution and possible fragmentation of the Explorer Plate.
Czoski, P. A.; Trehu, A. M.; Williams, M. C.; Dziak, R. P.; Embley, R. W.
UNAVCO Plate Boundary Observatory 2007 Student Field Assistant Program in the Alaska Region
NASA Astrophysics Data System (ADS)
The UNAVCO, Inc. Plate Boundary Observatory (PBO) Student Field Assistant Program strives to engage students in further study and careers in the Earth Sciences. Student Field Assistants from a variety of educational backgrounds ranging from high school graduates to master's level students spend a three to five month field season working in tandem with UNAVCO regional Field Engineers. The students work closely with senior staff to reconnaissance, install, and maintain a network of 875 permanent Global Positioning System (GPS) stations in one of the five PBO regions covering the western United States, including Alaska. Practical skills, such as power tool use, drilling, welding, firearms training, and proper field safety procedures, are taught and expected of the students. Installation and maintenance of new and existing GPS stations composes the bulk of the student's responsibilities and duties. When not in the field, students prepare gear and arrange logistics for site installations and maintenance as well as enter metadata and complete installation reports from recently constructed sites. An understanding of the operations of the GPS receivers and the scientific benefit of the network allows for an appreciation and great attention to detail during installation of the sites. Student assistance in the Alaska region during 2007 PBO AK field season was critical to the successful installation of 36 new GPS stations throughout Alaska. Significant benchmarks of the field season included installing six logistically difficult stations in Prince William Sounds, completing the Denali Fault GPS network, four new tiltmeters on Akutan Volcano, completing all installs on the Seward Peninsula as well as several new GPS stations throughout the western interior of the state. Alaska is a prominent area for much movement and deformation as the Pacific Plate subducts beneath the North American Plate resulting in an area of high volcanic activity and heightened crustal deformation. The GPS network that is being constructed aims to better understand much of these earth processes and their effects. To date, the Alaska Region has recently completed its 4th field season and has installed 106 out of a planned 140 stations. During Year 5 of the PBO project, the Alaska PBO regional office will complete the installation of all remaining 34 planned GPS stations including 12 stations on Unimak Island. The 2008 field season will be the last year in the installation phase and will incorporate maintenance of some of the first GPS stations installed in the network during the first and second years of the five year project.
Marzulla, A.; Gasparich, S.; Pauk, B.; Feaux, K.; Jackson, M.
Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice
Advances in the technology for exploiting resources of the oceans, particularly recovery of hydrocarbons and minerals in deep water, is benefiting a growing number of nations. At the same time, however, economic and political pressures have induced concern and there is now a much increased emphasis on jurisdiction to divide the offshore areas between the 132 coastal nations. Negotiations affect research operations at sea and, in consequence, marine scientists have been made aware of offshore problems as highlighted by the Law of the Sea Treaty (UNCLOS III) and complications arising from the legal versus scientific definitions of continental shelves and margins. The first major offshore boundary case of international scope where plate tectonics has constituted a significant argument is the one recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Of the two parties, Libya placed the greatest emphasis on this concept as a means to determine natural prolongation of its land territory into and under the sea. Tunisia contested Libya's use of the whole of the African continental landmass as a reference unit; in Tunisia's view, considerations of geography, geomorphology, and bathymetry are at least as relevant as are those of geology. In its landmark judgment (February 1982) - which almost certainly will have far-reaching consequences in future such boundary delimitation cases - the court pronounced that It is the outcome, not the evolution in the long-distant past, which is of importance, and that it is the present-day configuration of the coasts and sea bed which are the main factors to be considered, not geology.
Stanley, D.J.
NSDL National Science Digital Library
Students will go over the main points of plate tectonics, including the theory of continental drift, different types of plate boundaries, seafloor spreading, and convection currents. We have been spending time learning about plate tectonics. We have discussed the theory of continental drift, we have talked about the different types of plate boundaries, we have also learned about seafloor spreading and convection currents. Plate Boundary Diagram Now is your chance ...
Rohlfing, Mrs.
A Magmatic System as an Indicator of Tectonic Stresses around Plate Boundary; Crustal Deformation in and around Izu-Oshima Japan Derived from Continuous GPS Measurments
The area around Izu peninsula Japan is situated in a boundary region between the Philippine Sea plate and a continental plate. There are a number of things that bring a complexity to the tectonic setting of the region; the proximity to a triple junction of a continental and two oceanic plates and a volcanic front running through being accompanied by
M. Murakami
Tidal calibration of Plate Boundary Observatory borehole strainmeters: Roles of vertical and shear coupling
NASA Astrophysics Data System (ADS)
A multicomponent borehole strainmeter directly measures changes in the diameter of its cylindrical housing at several azimuths. To transform these measurements to formation strains requires a calibration matrix, which must be estimated by analyzing the installed strainmeter's response to known strains. Typically, theoretical calculations of Earth tidal strains serve as the known strains. This paper carries out such an analysis for 12 Plate Boundary Observatory (PBO) borehole strainmeters, postulating that each of the strainmeters' four gauges responds ("couples") to all three horizontal components of the formation strain tensor, as well as to vertical strain. Orientation corrections are also estimated. The fourth extensometer in each PBO strainmeter provides redundant information used to reduce the chance that coupling coefficients could be misleadingly fit to inappropriate theoretical tides. Satisfactory fits between observed and theoretically calculated tides were obtained for three PBO strainmeters in California, where the calculated tides are corroborated by other instrumentation, as well as for six strainmeters in Oregon and Washington, where no other instruments have ever recorded Earth tidal strain. Several strainmeters have unexpectedly large coupling coefficients for vertical strain, which increases the strainmeter's response to atmospheric pressure. Vertical coupling diminishes, or even changes the sign of, the apparent response to areal strain caused by Earth tides or deep Earth processes because near the free surface, vertical strains are opposite in sign to areal strain. Vertical coupling does not impair the shear strain response, however. PBO borehole strainmeters can provide calibrated shear strain time series of transient strain associated with tectonic or magmatic processes.
Roeloffs, Evelyn
The EarthScope Plate Boundary Observatory: Bringing Low Latency Data From Unimak Island, Alaska
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, will complete the installation of a fourteen station GPS network on Unimak Island, Alaska in August, 2008. The primary data communications goal of the project is to design and implement a robust data communications network capable of downloading 15-sec daily GPS files and streaming 1 Hz GPS data, via Ustream, from Unimak Island to three data relay points in the Aleutian chain. As part of the permitting agreement with the landowner, PBO will co-locate the GPS stations with existing USGS seismic stations. The technical challenges involved in optimizing the data communications network for both the GPS data and the seismic data will be presented. From Unimak island, there will be three separate data telemetry paths: 1) West through a radio repeater on Akutan volcano to a VSAT in Akutan village, 2) East through a radio repeater to a T1 connection in Cold Bay, AK, 3) South through a radio repeater to a VSAT at an existing PBO GPS station in King Cove, AK. The difficulties involved in the project include complex network geometries with multiple radio repeaters, long distance RF transmission over water, hardware bandwidth limitations, power limitations, space limitations, as well as working in bear country on an incredibly remote and active volcano.
Feaux, K.; Mencin, D.; Jackson, M.; Gallaher, W.; Pauk, B.; Smith, S.
Three-dimensional stability by global modes in the flat plate boundary-layer flow
NASA Astrophysics Data System (ADS)
The stability of the flat-plate boundary-layer flow is studied by means of three-dimensional eigenmodes of the linearized Navier--Stokes equations obtained by linearization about the steady state. The disturbance variables are approximated using a Fourier--Chebyshev collocation technique in inhomogeneous directions. Given the large size of the generalized eigenvalue problem we employ Arnoldi iterations using |ARPACK|. By expanding the flow disturbance variables in the basis of eigenmodes the growth potential is revealed by the computation of the optimal initial condition. This yields a low-dimensional model of the flow and a unified view on its stability characteristics. We discuss three different mechanisms associated with the non-normality of the operator: The lift-up mechanism is a componentwise non-normality where momentum is transferred from the spanwise to the streamwise velocity component. The Orr mechanism provides, through structures leaning against the shear, an efficient way of obtaining short time growth while borrowing energy from the mean flow, transferring momentum from the streamwise component to the wall-normal component. The TS mechanism is related to the streamwise non-normality where initial disturbances are located upstream and wavepacket propagation leads to a large energy gain downstream.
�kervik, Espen; Brandt, Luca; Henningson, Dan S.
Surface cracks as a long-term record of Andean plate boundary segmentation
NASA Astrophysics Data System (ADS)
Meter-scale surface cracks throughout the northern Chilean and southern Peruvian forearcs provide a long-term record of seismic segmentation along the Andean plate boundary. The cracks, mapped on high-resolution satellite imagery, show strong preferred orientations over large regions and the mean strikes of cracks vary systematically as a function of position along the margin. The spatial scale of this variation suggests that stress fields operating with similar dimensions, namely those produced by strong subduction zone earthquakes, are primarily responsible for crack evolution. The orientations of cracks are consistent with the static and dynamic coseismic stress fields calculated for several recent and historical earthquakes on distinct segments of the subduction interface. Field observations indicate that the cracks have experienced multiple episodes of opening and proximal age evidence suggests that they represent deformation as old as several hundred thousand years. We invert the crack orientation data to solve for plausible slip distributions on the Iquique, Chile segment of the margin (19�--23� S), which last ruptured in a M~8--9 event in 1877. We find that concentrations of coseismic slip resolved by the inversion coincide spatially with negative gravity anomalies, consistent with recent studies correlating subduction zone earthquake slip with forearc structure. These results suggest that distinct seismic segments or asperities on the subduction interface define characteristic earthquakes with rupture dimensions and magnitudes that are similar over many seismic cycles.
Loveless, J. P.; Allmendinger, R. W.; Pritchard, M. E.
The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries
NASA Technical Reports Server (NTRS)
The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.
Solomon, Sean C.
Nature and distribution of geological domains at the Africa-Eurasia plate boundary off SW Iberia and regional geodynamic implications
NASA Astrophysics Data System (ADS)
We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along two regional wide-angle seismic transects, one running NW-SE from the Horseshoe to the Seine abyssal plains, and the other running N-S from S Portugal to the Seine Abyssal Plain, combined with previously available information. The seismic velocity and density structure at the Seine Abyssal Plain and the internal Gulf of Cadiz indicates the presence of a highly heterogeneous oceanic crust, similar to that described in ultra-slow spreading centers, whereas in the Horseshoe and Tagus abyssal plains, the basement structure resembles that of exhumed mantle sections identified in the Northern Atlantic margin. The integration of all this new information allows defining the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental break-up (Late Jurassic); and (3) the Gorringe Bank domain, mainly made of rocks exhumed from the mantle with little synchronous magmatism, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain. The formation and evolution of these three domains during the Mesozoic is key to understand the sequence of events that occurred during the first stages of opening of the Northern Atlantic.
Mart�nez-Loriente, Sara; Sallar�s, Valent�; Gr�cia, Eul�lia; Bartolome, Rafael
Kinematics of the New Zealand plate boundary: Relative motion by GPS across networks of 1000 km and 50 km spacing
NASA Technical Reports Server (NTRS)
The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the field investigations are given in the appendix. An overview of the 1992 GPS field program is also given in the appendix.
Meertens, Charles M.; Rocken, Christian; Perin, Barbara; Walcott, Richard
Changes in plate boundary kinematics: Punctuated or smoothly varying � Evidence from the mid-Cenozoic transition from lithospheric extension to shortening in New Zealand
NASA Astrophysics Data System (ADS)
The marine magnetic anomaly record and plate kinematics derived from that data provide evidence of numerous cases of significant changes in plate motions and plate interactions. However, in most cases the temporal resolution provided by the marine record does not discriminate between punctuated (abrupt) or smooth variations in plate motions. During a 10 million year period (~ 30 Ma to 20 Ma), the Euler poles (stage poles) describing Australia-Pacific relative plate motion migrated more than 20� in latitude. The New Zealand segment of the plate boundary is close to the location of the Euler poles and their migration making the tectonics of its plate boundary structures particularly sensitive to the history of plate kinematics. Based on the rapid southward migration of the Euler (stage) poles from north of New Zealand to south of the landmass, there is an expected rapid, migrating transition from an extensional (stage pole north of the site) to transpressional (stage pole south of the site) plate boundary system. The geologic signature of this rapid change in plate boundary kinematics is preserved in the stratigraphic record of a suite of basin deposits that span the latitudinal sweep of the migrating Euler poles. Analyses of these deposits indicate that the timing of the transition from extensional to transpressional tectonics shows a continuous and systematic southward sweep, indicating that the changes in Australia-Pacific plate motions during the 30 Ma-20 Ma interval were smoothly continuous and not punctuated.
Furlong, Kevin P.; Kamp, Peter J. J.
The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries
NASA Technical Reports Server (NTRS)
The focus of the research was in two broad areas during the most recent 6 month period: the nature and dynamics of time-dependent deformation along major seismic zones, including the influence of irregularities in fault geometry on the earthquake cycles, and the processes contributing to the state of stress and rates of strain in plate interior regions. The principal findings of the research to date are described.
Solomon, Sean C.
Styles of accretion along the oblique convergent margin of Southern Chile
The continental margin of Southern Chile, between 50 to 58�S, is shaped by convergence processes between Antarctic and Scotia\\/South America plates which produce a narrow and elevated subduction complex. The plate boundary is roughly orthogonal to the slip vector to the north where the accretionary wedge is narrow and there is no evidence of a recent forearc basin. In this
M. F. Loreto; A. Polonia; L. Torelli; C. R. Ranero
Influence of porous-coating thickness on the stability and transition of flat-plate supersonic boundary layer
NASA Astrophysics Data System (ADS)
In the present study, we examined, both experimentally and theoretically, the influence of porouscoating thickness on the stability and laminar-turbulent transition of flat-plate supersonic boundary layer at free-stream Mach number M? = 2. A qualitative agreement between the data calculated by the linear theory of stability and the experimental data on the transition obtained for models with different porous-coating thicknesses was established. We show that with decreasing (within a certain interval) the porouscoating thickness the boundary layer becomes more stable to perturbations, and the laminar-turbulent transition, more delayed.
Gaponov, S. A.; Ermolaev, Yu. G.; Kosinov, A. D.; Lysenko, V. I.; Semenov, N. V.; Smorodskii, B. V.
A Geodetic Strain Rate Model for the Pacific-North American Plate Boundary, western United States
NASA Astrophysics Data System (ADS)
We present a model of crustal strain rates derived from GPS measurements of horizontal station velocities in the Pacific-North American plate boundary in the western United States. The model reflects a best estimate of present-day deformation from the San Andreas fault system in the west to the Basin and Range province in the east. Of the total 2,846 GPS velocities used in the model, 1,197 are derived by ourselves, and 1,649 are taken from (mostly) published results. The velocities derived by ourselves (the "UNR solution") are estimated from GPS position time-series of continuous and semi-continuous stations for which data are publicly available. We estimated ITRF2005 positions from 2002-2011.5 using JPL's GIPSY-OASIS II software with ambiguity resolution applied using our custom Ambizap software. Only stations with time-series that span at least 2.25 years are considered. We removed from the time-series continental-scale common-mode errors using a spatially-varying filtering technique. Velocity uncertainties (typically 0.1-0.3 mm/yr) assume that the time-series contain flicker plus white noise. We used a subset of stations on the stable parts of the Pacific and North American plates to estimate the Pacific-North American pole of rotation. This pole is applied as a boundary condition to the model and the North American - ITRF2005 pole is used to rotate our velocities into a North America fixed reference frame. We do not include parts of the time-series that show curvature due to post-seismic deformation after major earthquakes and we also exclude stations whose time-series display a significant unexplained non-linearity or that are near volcanic centers. Transient effects longer than the observation period (i.e., slow viscoelastic relaxation) are left in the data. We added to the UNR solution velocities from 12 other studies. The velocities are transformed onto the UNR solution's reference frame by estimating and applying a translation and rotation that minimizes the velocities at collocated stations. We removed obvious outliers and velocities in areas that we identified to undergo subsidence likely due to excessive water pumping. For the strain rate calculations we excluded GPS stations with anomalous vertical motion or annual horizontal periodicity, which are indicators of local site instability. First, we used the stations from the UNR solution to create a Delaunay triangulation and estimated the horizontal strain rate components (and rigid body rotation) for each triangle in a linear least-squares inversion using the horizontal velocities as input. Some level of spatial damping was applied to minimize unnecessary spatial variation in the model parameters. The strain rates estimates were then used as a priori strain rate variances in a method that fits continuous bi-cubic Bessel spline functions through the velocity gradient field while minimizing the weighted misfit to all velocities. A minimal level of spatial smoothing of the variances was applied. The strain rate tensor model is shown by contours of the second invariant of the tensor, which is a measure of the amplitude that is coordinate frame independent. We also show a map of the tensor style and of the signal-to-noise ratio of the model.
Kreemer, C.; Hammond, W. C.; Blewitt, G.; Holland, A. A.; Bennett, R. A.
The EarthScope Plate Boundary Observatory (PBO) Facility: Innovations, Transformations, and Impact
NASA Astrophysics Data System (ADS)
The word 'transformation' is not used lightly in science. However, the transformative nature of the EarthScope Plate Boundary Observatory facility on the science community is large and measurable. The impact of the creation, execution and delivery of the PBO resulted in radical changes in the way the geodesy community views permanent, continuously operating (and often) real-time GPS and strain networks, open data policies, and the ability for consortium based facilities, such as UNAVCO, to manage and deliver on large National Science Foundation investments. Our presentation will explore these innovations and transformations from the community, facility, and science perspectives. In the genesis of the EarthScope proposal there was a distinct shift away from the PBO being managed and constructed by prominent PI's within the community to a vesting of the responsibility and authority in UNAVCO to execute on behalf of the entire community. This tipping away from individual PI concerns towards a communal behavior allowed the construction of a facility based on broad input from, and equal access for, any member of the geodesy community. The open and transparent nature of EarthScope, including the open data policy for both facility and PI derived data was truly transformative. One of the key tenants of the PBO was strict adherence to not redesigning unless absolutely necessary. For example PBO monumentation and data processing practices were adopted wholesale from the SCIGN project, while the station selection, project management, permitting practices, data downloading, metadata, and, data communications were refactored for optimum use for the broader geodesy community and to scale with the large geography that confronted PBO. The PBO strainmeter network, one of the largest in the world, started by looking at the procedures of 30 years of heterogeneous installations around the word then crafted, created, and amalgamated new drilling, grouting, installation, and data processing procedures that allowed the project to deal with a compressed installation time line and the varying climactic and geological terrains in the Western US. The science that has come from the PBO deployments includes not only estimates of the secular deformation field across important structures in the active Western US but has provided a full kinematic and dynamic picture of the Pacific and North American Plate boundary interaction. The data registered from the PBO network has been used in diverse studies including determination of the asthenospheric density, temperature, and elastic moduli beneath the Western US (Ito and Simons, 2011), snow depth sensing using GPS multipath (Larson and Nievinski, 2013), continuous monitoring of the horizontal displacement gradient tensor field in Southern California (Holt and Shcherbenko, 2013), and using strainmeter data to constrain the magma reservoir beneath the Yellowstone (Luttrell, 2013). There is little doubt that the EarthScope PBO has met and exceeded its science goals, however what is exciting and transformative is the science that has resulted from the signals and the noise found in between these broad science goals.
Jackson, M. E.; Mencin, D.; Feaux, K.
Halfway There: An EarthScope Plate Boundary Observatory Progress Report
NASA Astrophysics Data System (ADS)
The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008, acquire radar imagery and geochronology as well as manage data for 209 previously existing continuous GPS stations through the PBO Nucleus project. As of September 2006, UNAVCO had completed half the PBO GPS stations, with 426 installed and data returned from 400 stations, and 60% of the PBO Nucleus stations have been upgraded. Highlights of the past year's work include the expansion of the Alaska subnetwork to nearly 70 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and is now being expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. UNAVCO is also installing and operating the largest borehole seismic/strainmeter network in North America, as well as tiltmeters and laser strainmeters. As of September 2006, 19 PBO borehole stations had been installed and two laser strainmeter stations were operating, with a total of 28 borehole stations and 3 laser strainmeters expected by the end of 2006. In response to direction from the EarthScope community, UNAVCO has installed a dense network of six stations along the San Jacinto Fault near Anza, California. During the fall of 2006, the first borehole stations will be installed on Mt. St. Helens, along with the first PBO borehole tiltmeters, and work will begin to densify the network near Parkfield. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network has now provided almost 150 GB of raw data, with special downloads of more than 15 GB of high-rate GPS data following the March 2006 Koryakia, Russia and May 2006 Tonga earthquakes. These GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 60 GB of raw data, which are available from the IRIS Data Management Center (DMC). The PBO strainmeter network has provided nearly 30 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/?pageid=88 and http://pboweb.unavco.org/?pageid=89 for more information on PBO GPS and strainmeter/seismic data products.
Jackson, M.; Anderson, G.; Blume, F.; Coyle, B.; Feaux, K.; Friesen, B.; Hafner, K.; Hasting, M.; Johnson, W.; Mencin, D.; Pauk, B.; Phillips, D.; Walls, C.; Prescott, W.
Cascadia slow slip events and earthquake initiation theories: Hazards research with Plate Boundary Observatory geodetic data (Invited)
NASA Astrophysics Data System (ADS)
The relationship of transient slow slip events (SSEs) to great earthquakes is a global focus of intense and critical hazards research. Plate Boundary Observatory (PBO) GPS and borehole strainmeter (BSM) networks in the Cascadia forearc provide detailed data that can be compared with simulations predicting how SSEs might evolve as a great earthquake approaches. Cascadia SSEs represent aseismic slip of a few cm in the direction of plate convergence over a period of days or weeks, in a depth range down-dip from the locked zone expected to generate the next great Cascadia subduction earthquake. During an SSE, shear stress borne in the SSE depth range is transferred up-dip at an above-background loading rate. If shear stress on the locked zone is continually accumulating, the daily probability of reaching a threshold failure stress is elevated during an SSE . Alternatively, if dynamic instability is due to ra