Using Dynamic Rupture Simulations to Investigate the Effects of Topography on Rupture Propagation along Branch Faults: Implications for the San Andreas and Garlock Faults

Evan O. Marschall, & Roby Douilly

Published September 11, 2022, SCEC Contribution #12265, 2022 SCEC Annual Meeting Poster #143

The San Andreas (SAF) and Garlock (GAF) fault intersection in Southern California represents the juncture of California's two longest faults. Paleoseismic studies have revealed that this section of the SAF has hosted some of the largest earthquakes in California (the ~M 7.9 1857 Fort Tejon earthquake) and is believed to have a recurrence interval of 100-150 yrs for events of M >7. Along this fault system, the SAF-GAF branch fault can impact rupture and determining whether an earthquake rupture will stop or propagate through this geometrical discontinuity is vital to the estimation of ground motion and seismic hazard. Numerical models of branch faults have described many of the factors that can affect the ability of rupture to propagate through those discontinuities. However, the fault dip angle and the surface topography are two factors that haven’t been fully explored. In this work we run simple planar models to isolate the effects of topography on the rupture process along branch faults. We model the fault system as a 40 km long main fault bisected by a 20 km branch fault at an angle of 50 degrees which is comparable to the angle between the SAF and GAR. We test 4 different topographie in regards to the branch fault, including a flat or zero topography case. We resolve fault stress for several different angles of constant regional stress. Preliminary results indicate that topography can introduce dynamic clamping and unclamping phases during the rupture. We observe that these dynamic phases can have effects on the rate of rupture propagation with a stress change in the order of ~1-2 MPa. This may indicate that these dynamic phases are secondary effects when compared to static stress changes in rupture path determination and may be sufficient enough to cause rupture if the branch fault is already close to failure. We will further investigate this issue by considering a variety of on fault stress conditions.

Key Words
Dynamic Rupture, San Andreas, Branch Faults, Topography

Citation
Marschall, E. O., & Douilly, R. (2022, 09). Using Dynamic Rupture Simulations to Investigate the Effects of Topography on Rupture Propagation along Branch Faults: Implications for the San Andreas and Garlock Faults. Poster Presentation at 2022 SCEC Annual Meeting.

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