Source parameters of a M4.8 and its accompanying repeating earthquakes off Kamaishi, NE Japan: Implications for the hierarchical structure of asperities and earthquake cycle

We determine the source parameters of a M4.9 ± 0.1 'characteristic earthquake' sequence and its accompanying microearthquakes at ∼50 km depth on the subduction plate boundary offshore of Kamaishi, NE Japan. The microearthquakes tend to occur more frequently in the latter half of the recurrence intervals of the M4.9 ± 0.1 events. Our results show that the microearthquakes are repeating events and they are located not only around but also within the slip area for the 2001 M4.8 event. From the hierarchical structure of slip areas and smaller stress drops for the microearthquakes compared to the M4.8 event, we infer the small repeating earthquakes rupture relatively weak patches in and around the slip area for the M4.8 event and their activity reflects a stress concentration process and/or change in frictional property (healing) at the area. We also infer the patches for the M4.9 ± 0.1 and other repeating earthquakes undergo aseismic slip during their interseismic period.