Preliminary Dynamic Models of Rupture Propagation Along the San Andreas Fault System Through the San Gorgonio Pass, CA

Tarnowski, Jennifer M. and Oglesby, David D.
[email protected]

We use numerical modeling to investigate the likelihood of a through-going earthquake along the San Andreas fault system in the San Gorgonio Pass (SGP). The SGP is a structurally complex area of Southern California often referred to as a “pinch-point” along the fault system, with several non-vertical and non-coplanar segments. It may or may not be a geometrical barrier that can slow or stop earthquake rupture propagation. The likelihood of through-going rupture in the SGP affects the maximum earthquake size in Southern California as well as the intensity and distribution of ground motion, with implications for seismic hazard. We use the finite element code FaultMod (Barall, 2009) to observe differences in rupture propagation and ground motion based on different input parameters in a simplified fault geometry of the SGP region. Models that include the San Bernardino, Garnet Hill, and Coachella Valley fault strands show that near-fault ground motion patterns are heterogeneous with pronounced asymmetry across the fault strands. Ground motion distribution farther from the strands varies with the hypocenter location. Under extremely simplified assumptions, it appears that rupture is possible in the SGP. However, the models presented here are the first in a series of test cases to develop more realistic models of rupture in the SGP that incorporate the complexity of fault geometry and stress distribution in the region.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013