Fig. 9
a P-wave and b S-wave velocity perturbations and c Vp/Vs ratios at 10, 15, 20, 30, 40, and 60 km depth. Velocity perturbations are the deviations from the average velocity at each depth. Gray curves represent the iso-depth contour of the PHS slab at each depth. Regions with a deviated weight sum of > 1000 are shown. Hypocenter (black dots) and LFE (red circles) distributions are shown in (c) (note that tectonic LFEs are not shown). White arrows at 15–40 km depth in (a) denote the high-velocity zone discussed in the text