A possible effect of an intermediate depth intraslab earthquake on seismic cycles of interplate earthquakes at a subduction zone

摘要

The effect of static stress perturbations due to an intermediate depth intraslab earthquake on seismic cycles of large interplate earthquakes at a subduction zone is examined through a numerical simulation using a laboratory-derived friction law. The frictional stress on a plate interface in a two-dimensional uniform elastic half-space model is assumed to obey a rate- and state-dependent friction law, and the plate interface is loaded by a steady plate motion, resulting in recurrence of large interplate earthquakes in the model. Static stress perturbations on the plate interface due to an intermediate depth intraslab earthquake with reverse fault type is introduced to the model. This model is set up so as to simulate seismic cycles at the Miyagi-Oki subduction zone, northeastern Honshu, Japan, where a large interplate earthquake is expected to occur and an intraslab earthquake of M = 7.1 took place in May, 2003. The simulation result indicates that the static stress changes due to the intraslab earthquake promote slip just below the interplate seismogenic zone, accelerating aseismic sliding there. This aseismic sliding generates stress concentration at the bottom of the seismogenic zone, often advancing the occurrence time of the next interplate earthquake. The shear-stress increases at aseismic slip regions with velocity-strengthening frictional property cannot be held and then aseismic sliding should take place to relax the increased stress. The present simulation result suggests that the promotion of aseismic sliding around the source area is important for evaluating the triggering effects of earthquakes. The conventional Coulomb failure stress approaches to the evaluation of the effect of static stress changes on seismic activity may be insufficient when static stress changes influence aseismic slip rates.