Fig. 1

(a) Location map of area explored in this study. Locations of our wide-angle seismic experiments are shown in black lines. Area located in the red rectangle is the target area for this study and is magnified in (c) and (d). The red star indicates the location of the seafloor borehole broadband seismometer (WP-2) employed by Shinohara et al. (2008). (b) Map showing half-spreading rates (Müller et al., 2008) in the Northwest Pacific Basin. The rate in the studied area exceeds 80 mm/yr. (c) OBS deployment map with topography data. Red circles indicate positions of OBSs. Larger ones (MTr6-79, MTr6-96, MTr8-7, and MTr8-15) are the OBSs whose record sections are shown in Fig. 2. MTr6-92/MTr8-13 is the same OBSs deployed at the intersection of two survey lines. (d) Paleomagnetic map around the survey area. Two survey lines are set perpendicular and parallel to the paleomagnetic lineation.