Fig. 6.

Vertical section of P-wave velocity structure and the aftershock distribution along the refraction profile (Nakahigashi et al., in preparation). The aftershocks within a 15-km-wide box on both sides along the profile are projected onto the seismic survey profile. The aftershocks indicated by orange circles have a distance less than 5 km from the profile. Contours and numerals indicate P-wave velocities. Contour interval is 0.4 km/s. The profile of the refraction survey (black line in Fig. 4) is parallel to the strike of the trench. Note a large exaggeration for the vertical axis. Red circles indicate the hypocenters of the aftershocks, and diameters of circles correspond to magnitudes. Inverted triangles indicated the projected position of the pop-up type OBSs. Most of the aftershocks occurred in the plate boundary region. There is no seismic-ity in the contact region of two oceanic plates.