Effects of Fault Geometry and Pre-Stress Loading for Scenarios of Earthquakes on the Eastern San Gorgonio Pass Region in CA using Dynamic Rupture Simulations

Roby Douilly, David D. Oglesby, Michele L. Cooke, & Jennifer L. Beyer

Published August 7, 2018, SCEC Contribution #8321, 2018 SCEC Annual Meeting Poster #208

Compilations of geologic data have illustrated that the right-lateral Coachella segment of the southern San Andreas Fault is past its average recurrence time period. On its western edge, this fault segment is split into two branches: the Mission Creek strand, and the Banning fault strand, of the San Andreas Fault. Depending on how rupture propagates through this region, there is the possibility of a through-going rupture that could lead to the channeling of damaging seismic energy into the Los Angeles Basin. The fault structures and rupture scenarios on these two strands are potentially very different, so it is important to determine which strand provides a more likely rupture path, and the circumstances that control the rupture path. In this study, we focus on the effect of different assumptions about fault geometry and initial stress pattern on the rupture process to test those scenarios and thus investigate the most likely path of a rupture that starts on the Coachella segment. We consider three types of fault geometry based on the Southern Community Fault Model (SCEC) and the Third Uniform California Earthquake Rupture Forecast (UCERF3), and we create a 3D finite element mesh for each. 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 it is more likely for the rupture to branch from the Coachella segment to the Mission Creek compared to the Banning fault segment, even if the closest connectivity is between the Coachella and Banning. For the regional stress distribution, we encounter cases of super-shear rupture for the SCEC fault geometry with the northeast dipping Coachella segment, and sub-shear rupture for the other two geometries. The fault connectivity at this branch system seems to have a significant impact on whether a through-going rupture is more likely to occur or not.

Citation
Douilly, R., Oglesby, D. D., Cooke, M. L., & Beyer, J. L. (2018, 08). Effects of Fault Geometry and Pre-Stress Loading for Scenarios of Earthquakes on the Eastern San Gorgonio Pass Region in CA using Dynamic Rupture Simulations. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)