carbonate-saturated fluids. These observations, combined with the extensive presence of shaley gouge even at low stratigraphic levels suggest that the Moab Fault was a conduit for fluid flow while supporting significant across-fault pressure differences. Fault seal prediction Clay smear is among the family of structures that detect fluid flow in sedimentary basins. Clay smear processes are applied to instances of cross-fault flow when porous and permeable rocks, specifically sandstones and shales, are cut by normal faults. According to Foxford et al., the most important feature of the Moab Fault zone from the standpoint of seal potential assessment is the nearly constant presence of at least one shaley gouge layer. The shale gouge ratio is one way to describe the amount of clay smear in a fault zone, and is simply defined as the percentage of shale/clay in the slipped interval. Shale gouge ratio, when applied to sand-shale sequences, indicates the proportion of phyllosilicate material expected to be incorporated into the fault rock. Thus it provides a measure of the seal capacity, as a shale layer in a fault zone may provide an effective seal to across-fault flow. Previous studies show that a shale gouge ratio of ~20% defines the boundary between sealing and non-sealing faults, with faults sealing at shale gouge ratios above this ‘cut-off’ value. Shale gouge is present in the Moab Fault at values >c. 20%, but varies depending on the location of the transect. References Geology of Utah Seismic faults of the United States Geography of Grand County, Utah