Spatial Variations in Slip on Corrugated Reverse Fault Surfaces

Faults are inherently non-planar at many scales; however, most seismic hazard analyses and geophysical methods of determining fault slip rates utilize highly simplified fault geometries. To better understand the slip behavior and seismic potential of non-planar fault surfaces, we present results from a suite of numerical models of faults with sinusoidal corrugations in the down-dip direction. Variations in wavelength, amplitude, and loading angle are introduced to determine the effects on slip behavior and seismic moment release. We find that corrugated faults, in general, slip less than planar faults and obliquely-loaded corrugated faults have less strike-slip than a planar fault with the same tip line dimensions. Short wavelength, large amplitude faults slip the least, with small changes in amplitude more strongly effecting short wavelength faults. Additionally, short wavelength, large amplitude faults accumulate mostly dip slip and, in some cases, may have an average net slip vector with the opposite sense of slip compared to their planar counterparts. This reversal in slip sense is the result of variations in resolved stress, as fault corrugations become sub-parallel to the oblique loading. Though seismic energy release can be larger for some non-planar surfaces relative to a planar surface, seismic energy release is always less for obliquely-loaded faults. While non-planar surfaces typically slip less than planar surfaces, some non-planar surfaces can release a greater amount of seismic energy relative to planar surfaces, due to a greater surface area. These results indicate a strong dependence of fault behavior on surface geometry and suggest that surface corrugation may dramatically alter slip distributions and slip rates. Therefore, models incorporating highly simplified fault surface geometry have the potential to significantly misrepresent fault slip rates. Example of modeled fault surface mesh with down-dip corrugations.