Seismicity on a fault controlled by rate- and state-dependent friction with spatial variations of the critical slip distance

We perform systematic simulations of slip using a quasi-dynamic continuum model of a two-dimensional (2-D) strike-slip fault governed by rate- and state-dependent friction. The depth dependence of the a - b and L frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations. Various realizations of heterogeneous L distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip. We demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault. We explore effects of three types of variable L distributions: (1) a depth-dependent L profile accounting for the variable width of fault zones with depth, (2) uncorrelated 2-D random distributions of L with different degrees of heterogeneity, and (3) a hybrid distribution combining the depth-dependent L profile with the 2-D random L distributions. The first type of L distribution, with relatively small L over the depth range corresponding to the seismogenic zone and larger L elsewhere, generates stick-slip events in the seismogenic zone and ongoing creep above and below that region. The 2-D heterogeneous parameterizations generate frequency-size statistics with event sizes spanning 4 orders of magnitude. Our results indicate that different degrees of heterogeneity of L distributions control (1) the number of simulated events and (2) the overall stress level and fluctuations. Other observable trends are (3) the dependency of hypocenter location on L and (4) different nucleation phases for small and large events in heterogeneous distributions.