Effects of Complex Fault Geometry on Rupture Path for Scenarios of Earthquakes in Southern California

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Roby Douilly

UC Riverside

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Online-only seminar via Microsoft Teams

Geologic data suggest that the Coachella segment of the southern San Andreas Fault is past its average recurrence time period. At its northern edge, this right-lateral fault segment branches into the Mission Creek and Banning strands of the San Andreas Fault. In this study, we examine the effect of different assumptions about fault geometry and initial stress pattern on the dynamic rupture process to test multiple rupture scenarios and thus investigate the most likely path(s) of a rupture that starts on the Coachella segment. We consider three types of fault geometry based on the Southern California Earthquake Center Community Fault Model, and we create a 3D finite element mesh for each of them. These three meshes are then incorporated into the finite element method code FaultMod to compute a physical model for the rupture dynamics. We use a slip-weakening friction law, and consider different assumptions of background stress, such as constant tractions and regional stress regimes with different orientations. Both the constant and regional stress distributions show that rupture from the Coachella segment is more likely to branch to the Mission Creek than to the Banning fault strand. The fault connectivity at this branch system seems to have a significant impact on the likelihood of a through-going rupture, with potentially significant impacts for ground motion and seismic hazard both locally and in the greater Los Angeles metropolitan area.

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