Small repeating earthquake activity, interplate quasi-static slip, and interplate coupling in the Hyuga-nada, southwestern Japan subduction zone

Small repeating earthquake (RE) analysis is a useful method for estimating interplate quasi-static slip, which is a good indicator of interplate coupling. We detected 170 continual-type interplate RE groups and then estimated the spatial variation in quasi-static slip in the Hyuga-nada over the past 17years. The RE activity in this region has different characteristics compared with that in the northeast Japan subduction zone, presumably reflecting differences in the subduction properties. Our results revealed that interplate coupling spatially changes along the trench-axis and dip-directiona phenomenon that cannot be resolved by land-based Global Positioning System (GPS) analysis. By comparing seismicity, the low-slip-rate areas correspond with the location of hypocenters and asperities for large-and moderate-sized interplate earthquakes, suggesting strong interplate coupling at these sites. These results indicate that the slip rate distribution estimated from RE activity is reliable and useful for assessing the potential of future large earthquakes.