Earthquake locations projected on the perspective view of the bathymetry and time-migrated sections. Hypocenter locations were projected on time-migrated section along four multi-channel reflection survey lines (Nakamura et al., 2011; 2013). Focal depths were converted to two-way times by using the 2-D velocity structure for the hypocenter determination. Stars and circles on the top perspective view indicate centroid locations of the December 7, 2012 Japan Trench doublet by GCMT and hypocenter locations of the earthquakes obtained from the OBS observations, respectively. Colors are coded by hypocentral depth. Earthquakes within 5 km from each survey line are projected on the time-migrated sections. Arrows on the cross sections indicate the top of the subducting oceanic crust and the oceanic Moho. Solid inverted triangles on the cross sections indicate normal faults associated with horst and graben structure and coinciding with the shallow earthquakes. The locations of the OBSs (diamonds) and JFAST drilling site (inverted triangle) (Chester et al. 2012) are also shown.