UC Riverside

We investigate how dynamic stresses can affect the occurrence of earthquakes in two regions in southern California. First we look at the San Gorgonio Pass (SGP) with 3D dynamic finite element models to investigate potential rupture paths of earthquakes propagating along faults in the western SGP. The SGP has several structurally complex regions because the San Andreas Fault splinters into many different fault strands and there are additional regional fault zones present in this location. 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 strand of the San Andreas Fault System and the San Gorgonio Pass Fault Zone. With simplified models, we find that nucleating on the San Bernardino strand does not produce through-going rupture, but that nucleation on the San Gorgonio Pass Fault Zone may produce through-going rupture in some scenarios. With more complex fault geometries, we find the stress and subsequent rupture propagation patterns are highly influence by the fault geometry and the initial stress field assumptions. Second, we look at the San Jacinto Fault Zone (SJFZ) for evidence of remote triggering. We find that, while rare, local events are triggered along the SJFZ by large magnitude remote events and that various methods are required to validate these examples of triggering.