Tobias Harvey, Brittany Angela Erickson, Jeremy Edward Kozdon

We present a computationally efficient numerical method for earthquake sequences that incorporates wave propagation during rupture. A vertical strike-slip fault governed by rate-and-state friction is embedded in a heterogeneous elastic half-space discretized using a high-order accurate Summation-by-Parts finite difference method. We develop a two solver approach: Adaptive time-stepping is applied during the interseismic periods and during coseismic rupture we apply a non-stiff method, which enables a variety of explicit time stepping methods. We consider a shallow sedimentary basin and explore model sensitivity to spatial resolution and the switching criteria used to transition between solvers. For sufficient grid resolution and switching thresholds, simulations results remain robust over long time scales. We explore the effects of full dynamics on earthquake sequences, comparing outcomes to their quasi-dynamic counterparts. The fully-dynamic ruptures are accompanied with higher stress concentrations, faster slip rates and rupture speeds, and produce seismic scattering in the bulk as waves propagate through and reflect off the basin edges. Because single-event dynamic simulations penetrate further into sediments compared to quasi-dynamic simulations, we hypothesize that the incorporation of inertial effects would produce sequences of only surface-rupturing events, as opposed to the subbasin events that emerge in purely quasi-dynamic scenarios. However, we find that with full dynamics present, the alternating sequence of subbasin and surface breaking ruptures is a persistent outcome. Thus an earthquake's potential to penetrate into shallow sediments should be viewed through the lens of the earthquake sequence, as it depends strongly on self-consistent initial conditions obtained from seismogenic cycling.