How Fault Geometry Affects Dynamic Rupture Models of Earthquakes in San Gorgonio Pass, CA

Abstract:

We use 3D dynamic finite element models to investigate potential rupture paths of earthquakes propagating along faults in the western San Gorgonio Pass (SGP) region of California. The SGP is a structurally complex area along the southern California portion of the San Andreas fault system (SAF). It has long been suspected that this structural knot, which consists of the intersection of various non-planar strike-slip and thrust fault segments, may inhibit earthquake rupture propagation between the San Bernardino and Banning strands of the SAF. The above condition may limit the size of potential earthquakes in the region. Our focus is on the San Bernardino strand of the SAF and the San Gorgonio Pass Fault zone, where the fault connectivity is not well constrained. We use the finite element code FaultMod (Barall, 2009) to investigate how fault connectivity, nucleation location, and initial stresses influence rupture propagation and ground motion, including the likelihood of through-going rupture in this region. Preliminary models indicate that earthquakes that nucleate on the San Bernardino strand and propagate southward do not easily transfer rupture to the thrust faults of the San Gorgonio Pass fault zone. However, under certain assumptions, earthquakes that nucleate along the San Gorgonio Pass fault zone can transfer rupture to the San Bernardino strand.