A structural contour map for the top of the northward subducting slab of the Philippine Sea Plate. The contour is made on the basis of the boundary between the higher V_P zone and the lower V_P area above it. Numbers represent depth below the surface. The red circle represents the surface projection of the high V_P/V_S body along profile A-A′ in Fig. 5. Bathymetry contour intervals are 500 m.