The effects of pre-stress assumptions on dynamic rupture with complex fault geometry in the San Gorgonio Pass, CA region

Jennifer M. Tarnowski, Christodoulos Kyriakopoulos, David D. Oglesby, Michele L. Cooke, & Aviel R. Stern

Awaiting Publication June 21, 2022, SCEC Contribution #11873

We use 3D dynamic finite element models to investigate potential rupture paths of earthquakes propagating along faults through the western San Gorgonio Pass (SGP), a structurally complex region along the San Andreas fault system (SAF) in southern California. We focus on the right-lateral San Bernardino strand of the SAF, the oblique thrust/right-lateral San Gorgonio Pass Fault Zone, and a portion of the right-lateral Garnet Hill strand of the SAF. We use the 3D Finite Element Method to model rupture propagation along a fault geometry that reflects current understanding of the local geometrical complexity, and is consistent with long-term loading and observed surface deformation. We test three different types of pre-stress assumptions: 1) constant tractions (assuming pure right-lateral strike-slip motion on the San Bernardino and Garnet Hill strands and oblique thrust/right-lateral strike-slip motion on the San Gorgonio Pass Fault Zone), 2) a uniform regional stress regime, and 3) long-term (evolved) stress from quasi-static crustal deformation modeling. Our results imply that under the more realistic regional stress and evolved stress assumptions, through-going rupture propagation from the southeast to northwest (i.e., from the Garnet Hill to the San Bernardino strand) may be more likely than through-going rupture in the reverse direction (from the San Bernardino strand to the Garnet Hill). The results may have implications for the earthquake potential in the region, as well as for ground motion in the Los Angeles Basin. The results also emphasize how fault geometry and stress patterns combine to influence rupture propagation on complex fault systems.

Key Words
San Gorgonio Pass, Dynamic Rupture, Earthquake Gate

Citation
Tarnowski, J. M., Kyriakopoulos, C., Oglesby, D. D., Cooke, M. L., & Stern, A. R. (2022). The effects of pre-stress assumptions on dynamic rupture with complex fault geometry in the San Gorgonio Pass, CA region. Geosphere, (awaiting publication).


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