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 model
the evolution of fault slip over long time periods (tens of thousands to hundreds of
thousands 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- and
state-dependent friction, is able to capture the observed short-term power-law clustering
behavior of earthquakes as well as model the two dominant obeserved modes of non-seismic
slip: steady creep and slow slip events (SSEs). The creeping sections of the fault system
are modeled as always at steady-state such that the slip-speed is a simple function of the
applied stresses, while SSE-generating sections use (an approximate form of) the mechanism
of Shibazaki and Iio (2003).

The work we will present here on the Cascadian subduction system is part of a larger project
to perform unified simulations of the entire western US plate boundary region. In it we use
realistic plate interface (and upper-plate fault system) geometries and distributions of
frictional properties to address issues such as: the relationship between the short-term
phenomena of earthquake triggering and clustering and the long-term recurrence of large
earthquakes implied by steady tectonic forcing; the interaction between fault sections with
different modes of slip prior to and in response to earthquakes (specifically including
possible iteractions between SSEs and large subduction earthquakes); interactions between
the main subduction thrust and upper plate faults; and the effects of quenched versus
dynamical heterogeneities on rupture processes.