Spatiotemporal Variations of Intermediate‐Depth Earthquakes Before and After 2011 Tohoku Earthquake Revealed by a Template Matching Catalog

We investigate spatiotemporal changes of intermediate-depth earthquakes in the double seismic zone beneath Central and Northeastern Japan before and after the 2011 magnitude 9 Tohoku earthquake. We build a template-matching catalog 1 year before and 1 year after the Tohoku earthquake using Hi-net recordings. The new catalog has a six-fold increase in earthquakes compared to the Japan Meteorological Agency catalog. Our results show no significant change in the intermediate-depth earthquake rate prior to the Tohoku earthquake, but a clear increase in both planes following the Tohoku earthquake. The regions with increased intermediate-depth earthquake activity and the post-seismic slips following the Tohoku earthquake are spatially separate and complementary with each other. Aftershock productivity of intermediate-depth earthquakes increased in both planes following the Tohoku earthquake. Overall, aftershock productivity of the upper plane is higher than the lower plane, likely indicating that stress environments and physical mechanisms of intermediate-depth earthquakes in the two planes are distinct.