Numerical Simulation of Episodic Aseismic Slip Events as Incomplete Nucleation of Seismic Slip Due to Heterogeneous Stress Distribution

Abstract

ABSTRACT Shear stress concentration at the deeper edge of a locked fault affects detachment of the fault, such as upward propagation of aseismic sliding, episodic aseismic slip events, and partial seismic rupture. Numerical simulations of earthquake cycles on a strike-slip fault were conducted using a rate- and state-dependent friction law to investigate the occurrence conditions of episodic aseismic slip events within a fault having uniform velocity-weakening friction. When the velocity-weakening zone is much wider than the critical nucleation zone size, a rupture that seismically or aseismically breaks a part of the velocity-weakening zone occurs during the interseismic period between large earthquakes. The partial seismic rupture results in a small earthquake, and the partial slow rupture results in an episodic aseismic slip event. The seismic or aseismic rupture is arrested in a low-shear-stress area, which is caused by the preceding large earthquake. The episodic aseismic slip events may be regarded as incomplete nucleation of an earthquake, because the rupture is arrested before acceleration to seismic slip, and this process may explain episodic aseismic slip events at seismogenic depths. The width of the area of preseismic sliding immediately before a simulated large earthquake is similar to that of episodic aseismic slip.