Fig. 4

Vertical profiles of velocity structure along the X axis shown in Fig. 2c. The contour interval of the velocity is 0.5 km/s. Black triangles and squares, and white circles indicate the locations of stations and earthquakes within 10 km from each section, respectively. Black bold lines indicate the location of the upper boundaries of the PAC (Nakajima et al. 2009) and PHS (Uchida et al. 2010). Red and magenta lines show the upper boundary of the PHS based on the present tomographic image and result of Ito et al. (2017), respectively. The crustal part of the PHS is indicated by areas labeled A. The other symbols are same as those defined in Fig. 3