Dynamic Models of Earthquake Rupture along branch faults of the Eastern San Gorgonio Pass Region in CA using Complex Fault Structure

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

Submitted August 1, 2017, SCEC Contribution #7379, 2017 SCEC Annual Meeting Poster #169

Compilation of geomorphic and paleoseismic 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. 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 is a more likely rupture path, and under which circumstances rupture will take either one. In this study, we focus on the effect of different assumptions about fault geometry and 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 two types of fault geometry based on the SCEC Community Fault Model and create a 3D finite element mesh. These two meshes are then incorporated into the finite element method code FaultMod to compute a physical model for the rupture dynamics. We use the slip-weakening friction law, and we consider different assumptions of background stress such as constant tractions and regional stress regimes of different orientations. Both the constant and regional stress distribution 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. For the regional stress distribution, we encounter cases of super-shear rupture for one type of fault geometry and sub-shear rupture for the other one. 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.

Douilly, R., Oglesby, D. D., Cooke, M. L., & Beyer, J. L. (2017, 08). Dynamic Models of Earthquake Rupture along branch faults of the Eastern San Gorgonio Pass Region in CA using Complex Fault Structure. Poster Presentation at 2017 SCEC Annual Meeting.

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