Configuration of subducting Philippine Sea plate and crustal structure in the central Japan region

A seismic experiment with 6 explosive sources and 391 seismic stations was conducted in August 2001 in the central Japan region. A large lateral variation of the thickness of sedimentary layer was observed. P‐wave velocity values below the sedimentary layer obtained were 5.3 km/s ∼ 5.8 km/s. P‐wave velocity values at the lower part of upper crust and lower crust are estimated to be 6.0 km/s ∼ 6.4 km/s and 6.6 km/s ∼ 6.8 km/s, respectively. Two clear later phases were observed at the record section of shot‐J5. The phases are interpreted to be reflected waves at the boundaries with depths of about 10–20 km and 20–35 km. The dip angle of the deep boundary is about 26°. The shallower reflector is interpreted to be a lithological boundary. The deeper reflector is the upper boundary of subducting Philippine Sea plate. The configuration of the subducting Philippine Sea slab was revealed.