Fig. 5

Structural interpretation of the reflection profile. a Final RTM section overlaid with the P-wave velocity (Matsubara et al. 2019). b Three-dimensional view of the interpreted reflection profile with the topography map in the Kanto region. The red and green lines corresponding to the eastward-dipping reflectors are interpreted as the top and bottom surfaces of the PHS crust, respectively. The depth of the PHS top surface is approximately consistent with that at intersecting points in previous studies (Sato et al. 2005; Kimura et al. 2006; Ishise et al. 2021). The orange dotted lines subparallel to the upper eastward-dipping reflector may be some unit boundaries within the PHS crust due to the crustal structures in the northward extension of the Izu-Bonin arc. The blue dotted line for the westward-dipping reflector is interpreted as the top of the PAC slab. The white lines indicate the en-échelon reflectors interpreted as the boundary between the upper and lower crust in the inland crust beneath the Kanto region. The yellow dot in (a) shows the depth of the PHS surface inferred by the seismic reflection survey (Sato et al. 2005). The green dot in (a) indicates the depth of the PHS slab surface inferred from repeated earthquakes (Kimura et al. 2006). The red and blue rectangles in (a) denote the depths of the PHS and PAC slab surfaces, respectively, which are read from the interpretation of receiver function analysis and repeating earthquakes (Igarashi et al. 2009). The magenta and black dashed lines indicate the PHS and PAC slab surfaces, respectively, in (a), and the translucent blue surface with contours shows the PAC slab surface in (b) of the previous interpretation of earthquake-based seismic tomography (Nakajima and Hasegawa 2006; Hirose et al. 2008; Nakajima et al. 2009). The black dots in (b) denote the sources projected to the RTM section from all earthquakes from the JMA catalog in the range of 10 km wide along the pseudo-survey line