Spatial Relationship between Interseismic Seismicity, Coseismic Asperities and Aftershock Activity in the Southwestern Kuril Islands

We investigate the spatiotemporal relationship between background seismic activity, coseismic asperities and aftershock activity in the southwestern Kuril Islands using high precision earthquake catalogue produced by Hokkaido University since 1976. Seismicity maps clearly indicate that coseismic asperity patches correspond to low seismic activity regions surrounded by high activity areas. This seismicity pattern in and around the asperity does not vary with time, which may suggest invariant stable frictional conditions in the temporal domain. We infer that these observations reflect the frictional nature of the asperity and its surrounding area. This spatial variation of seismic activity may be due to the variations of the yielding threshold point to the shear stress for earthquake faulting, which is due to the spatial variation of frictional parameters on the plate interface. It is feasible to recognize unknown asperities from epicenter distributions during the interseismic period. A similar relationship between asperity distribution and aftershock activity might also be due to the frictional variations on the plate interface.