Interaction between seismic and aseismic slip along a transcurrent plate boundary: a model for seismic sequences

Abstract

A model is proposed which may explain the multiple occurrence of earthquakes which is often observed in the same seismogenic region. Such earthquake sequences or swarms may consist of events several tens of kilometres apart in space and a few days to months apart in time. The model considers a long, vertical strike-slip fault embedded in an elastic half-space. The fault is heterogeneous with respect to strength and to slip style (seismic or aseismic) and is subject to a slowly increasing ambient shear stress. We assume that conditions for stable aseismic slip are present in a part of the fault plane together with unstable asperities. The failure of an asperity, producing one earthquake of the sequence, is assumed to produce the onset or the acceleration of a seismic slip on a distant area of the fault, in proximity to another asperity. The conditions under which the latter asperity may fail, producing another earthquake of similar magnitude, are studied as functions of ambient stress rate, asperity strength, amount of aseismic slip, and aseismic slip area. It is found that the effect of aseismic slip can be remarkable in anticipating the occurrence of the second earthquake.