Map (a) and vertical cross-sectional views (b) of hypocenters for X phases. Station N.SAMH and hypocenters are plotted as red inverted triangle and stars, respectively. Dots in (a) denote background seismicity in the subducting crust. Seismicity within 10 km from line A-B is shown in (b). The black line in (b) shows the upper surface of the Pacific slab (Nakajima et al. 2009b).