Fig. 4.

Final hypocenter distribution (March 12th–March 19th, 2011) derived by using the double-difference method with bathymetry. The inverted red triangles indicate the positions of the pop-up type OBSs and the land seismic station used for this study. The circles filled with color represent hypocenters. The depth of events is color-coded. The diameters of the circles are proportional to the magnitudes. Grey circles indicate epicenters of aftershocks determined by the JMA for the same period. Thick line indicates the profile of the seismic survey. Red contours indicate depths of surface of the subducting Pacific plate by a model estimated hypocenter distribution and seismic structures using OBSs. No exaggeration for vertical direction is applied. In the vertical section, the concentration of the aftershocks in depths of 5–30 km is clearly recognized. From the W-E vertical cross section, the aftershocks become deeper westward.