Earthquake distribution obtained in this study. Dots and open circles indicate the locations of events within the upper plane and lower plane of the DSZ, respectively. Open triangles indicate the locations of reverse-fault- or strike-slip-type events with the P-axis orientation ranging from the E-W to the NE-SW directions. Solid and broken curves are the same as in Fig. 1. An “X” indicates the deepest event detected in this region, with the exception of the deep intra-Pacific-slab events (see discussion in Section 3). (a) Epicentral distribution of earthquakes located in this study. Earthquakes deeper than 30 km are shown. Symbols A to J indicate the rectangle areas used for the cross-sections in (b). (b) Vertical cross-sections of hypocenters (depth from 0 to 100 km) within each rectangular area indicated in (a). Solid and broken curves show the upper surface of the PHS plate (Miyoshi and Ishibashi, 2004). Thick bars above each box indicate land areas.