Post-seismic and interseismic fault creep II: transient creep and interseismic stress shadows on megathrusts

Abstract

We use idealized subduction megathrust models to examine aseismic, frictional fault creep throughout the interseismic period. We consider rate-dependent and rate- and state-dependent friction. When there is significant post-seismic creep surrounding locations of coseismic slip, the creep rates surrounding an asperity may be lower than the plate convergence rate late in the seismic cycle. This lowering of the creep rates is due to stress shadows forming around the interseismically locked asperities. The size of the stress shadows increases as there is more transient post-seismic creep. Larger asperities produce larger interseismic stress shadows, and multiple asperities can act together to produce a stress shadow larger than the sum of the effects of the individual asperities. For rate-state frictional megathrusts, there is a wide range of transient post-seismic creep that occurs: from pulses of post-seismic creep with decreasing creep rates through time, to delayed post-seismic creep. Delayed post-seismic creep may occur well into the interseismic period, with transient creep lasting over a significant portion of the seismic cycle. Delayed post-seismic creep is generally favoured in velocity strengthening regions with either a larger magnitude of the frictional direct effect or a larger effective normal stress. In addition, regions of the fault undergoing delayed post-seismic creep must be above steady state following coseismic slip.