largest release of elastic strain energy since the 1957/1964 series of shocks on the Aleutian/Alaska Trench. The southeastern (Java) portion of the Sunda Trench extends from the Sunda Strait in the west to Bali Basin in the east. The convergence of relatively old oceanic crust is occurring at a rate of per year in the west portion and per year in the east, and the dip of the Benioff Zone (the angle of the zone of seismicity that defines the down-going slab at a convergent boundary) is around 50° and extends to a depth of approximately . Pre-instrumental events were the large to very large events of 1840, 1867, and 1875, but unlike the northwestern Sumatra segment, no megathrust earthquake has occurred on the Java segment of the Sunda Trench in the last 300 years. Earthquake The earthquake was the result of thrust faulting at the Sunda Trench. A rupture length of approximately (and an unusually low rupture velocity of per second) resulted in a duration of about 185 seconds (just over three minutes) for the event. The shock was centered from the trench, and about from the south coast of the island. A comparison was made with the earlier 2002 Sumatra earthquake, a M7.5 submarine earthquake of a similar size that also occurred along the Sunda Arc and at a shallow depth, but one that did not result in a tsunami. The large and damaging tsunami that was generated was out of proportion relative to the size of the event, based on its short-period body wave magnitude. The Indonesian Meteorological, Climatological, and Geophysical Agency assigned a magnitude of 6.8, and the United States Geological Survey (USGS) reported a similar value of 6.1 (both body wave magnitude) that were calculated from short-period seismic waves (1–2 seconds in the case of the USGS). The USGS then presented a moment magnitude of 7.2 that was calculated from 5–100-second surface waves, and Harvard University subsequently revealed that a moment magnitude of 7.7 had been resolved based on even longer 150-second surface waves. Intensity In tsunami prone regions, strong earthquakes serve as familiar warnings, and this is especially true for earthquakes in Indonesia. Previous estimates of the tsunami hazard for the Java coastline may have minimized the risk to the area, and to the northwest along the Sumatran coast, the risk is substantially higher for tsunami, especially near Padang. Previous events along the coast