Poster #160, Fault and Rupture Mechanics (FARM)

Dynamic rupture modeling of coseismic interactions on orthogonal strike-slip faults

Julian C. Lozos
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Poster Presentation

2020 SCEC Annual Meeting, Poster #160, SCEC Contribution #10678
The San Andreas Fault System is dominated by right-lateral strike-slip faulting. However, a large number of smaller orthogonal left-lateral structures also exist. Some, such as the Garlock Fault or Pinto Mountain Fault, are large enough to be mapped without having had a historic earthquake. However, the existence of other smaller orthogonal structures is often highlighted only when they rupture in conjunction or sequence with a larger mapped fault. The 2019 Ridgecrest sequence, which included a M6.4 rupture on a left-lateral fault followed 34 hours later by a M7.1 earthquake on an orthogonal right-lateral fault, exemplifies this. The Ridgecrest example raises questions as to what conditions ...led to the source faults rupturing in two closely-spaced earthquakes as opposed to one single larger event. That extends to broader questions about general behaviors of orthogonal strike-slip faults as earthquake gates: what conditions might make them rupture together versus separately, how likely is a rupture on one fault to activate a large cross-fault, and is this persistent behavior versus something changes over multiple earthquake cycles? Here, I use the 3D finite element method to simulate dynamic ruptures on orthogonal strike-slip fault systems with several geometrical configurations. In models with uniform initial stresses on both faults, which isolate the effects of fault geometry, I find that a stopping phase from rupture hitting the end of one fault is necessary to initiate rupture on the other. A rupture on one fault that crosses the other and continues on does not activate the second fault. I compare this set of models to ones in which the fault system is in a regional stress field, which produces different initial stresses on each fault.