Modeling a Wide Spectrum of Fault Slip Behavior in Cascadia With the Earthquake Simulator RSQSim

Through the judicious use of approximations, earthquake simulators hope to accurately modelthe evolution of fault slip over long time periods (tens of thousands to hundreds ofthousands of years) in complicated regional- to plate-boundary-scale systems of faults. RSQSim is one such simulator which, through its use of an approximate form of rate- andstate-dependent friction, is able to capture the observed short-term power-law clusteringbehavior of earthquakes as well as model the two dominant obeserved modes of non-seismicslip: steady creep and slow slip events (SSEs). The creeping sections of the fault systemare modeled as always at steady-state such that the slip-speed is a simple function of theapplied stresses, while SSE-generating sections use (an approximate form of) the mechanismof Shibazaki and Iio (2003). The work we will present here on the Cascadian subduction system is part of a larger projectto perform unified simulations of the entire western US plate boundary region. In it we userealistic plate interface (and upper-plate fault system) geometries and distributions offrictional properties to address issues such as: the relationship between the short-termphenomena of earthquake triggering and clustering and the long-term recurrence of largeearthquakes implied by steady tectonic forcing; the interaction between fault sections withdifferent modes of slip prior to and in response to earthquakes (specifically includingpossible iteractions between SSEs and large subduction earthquakes); interactions betweenthe main subduction thrust and upper plate faults; and the effects of quenched versusdynamical heterogeneities on rupture processes.