A numerical study on seismic coupling along subduction zones using a laboratory-derived friction law

Abstract

A numerical simulation study is performed to examine the effect of frictional characteristics of the boundary between a continental plate and a subducting oceanic plate on the seismic coupling between them. We consider a dip-slip fault in a 2-D uniform elastic half-space. The frictional force following a rate- and state-dependent friction law is assumed to act on the fault plane or the plate boundary, on which the values of friction parameters are varied with depth. Simulation results show that great earthquakes repeatedly occur at a shallower part of the plate boundary and stable sliding occurs at a deeper part. Seismic coupling is quantitatively discussed in terms of the seismic coupling coefficient defined by the seismic slip divided by the total amount of the seismic and aseismic slip. The critical fault length required for the occurrence of unstable slip is found to be proportional to the characteristic slip distance and inversely proportional to the coefficient of slip-rate dependence of the steady-state friction. The seismic coupling coefficient is relatively larger (0.6 to 0.8) when the length of the seismogenic zone is much longer than the critical fault length, while the seismic coupling coefficient becomes zero when the seismogenic zone length is close to or shorter than the critical fault length. In the latter case, slow or silent earthquakes are expected to occur. It is further found that spatially non-uniform distributions of friction parameters tend to weaken the seismic coupling.