Generation Mechanisms of Intermediate‐Depth and Deep Earthquakes in Southwestern Japan: Implications for the Tearing or Thinning of the Pacific Slab

Abstract

We performed a stress tensor inversion using focal mechanisms from intermediate‐depth and deep earthquakes to estimate the stress regime of the Pacific slab beneath southwestern Japan. We focused on the temporally averaged stress field derived from the recent 28‐year data set of the F‐net CMT solutions. Across a large portion of the study region, the estimated axes show a generally similar pattern consistent with a down‐dip compression regime. The axes are oriented parallel to the subduction direction of the Pacific slab, rather than to the maximum dip direction of the slab, suggesting that a resistance force likely acts on the subducting slab. In contrast, for the regions beneath Takayama and Wakasa Bay, the optimal axes are nearly horizontal and approximately parallel to the slab strike, trending N31.4°E and N10.4°W, respectively. Our results support models proposing the tearing or thinning of the Pacific slab.