Figure 8

Three-dimensional perspective view of crustal structures along northwestern (this study) and western (Arai et al.2013) profiles. P wave velocities for the upper crust (down to 10-km depth) are shown by color contours, and collisional boundaries and reflectors are shown by black solid lines. The Honshu arc consists of a horizontally homogenous layer for the upper 4-km crust (northwestern profile), which contrasts with the complex structure to the southeast (western profile). Here, the accreted crustal blocks of the IBA, which have a high velocity (green-blue parts with Vp above 6.0 km/s), are separated by dipping collisional boundaries that are accompanied by a lower-velocity sediment layer (red-orange parts with Vp below 5.0 km/s). The main body of the Kofu granitic complex (KGC), reportedly generated by partial melting of the subducted middle/lower crust of the IBA (e.g., Tamura et al. 2010), is situated at depths greater than 4 km but forms a bump just beneath the Kofu Basin (red lines).