Fig. 2

a Locations of lines used to measure contraction amounts. Blue, green, red, and purple lines on the PHS slab were situated along the Nankai Trough shown by the thick gray line at 3, 4, 5, and 6 Ma, respectively, under the assumption of plate motion (see text). Each colored line has a tick every 100 km. Contour lines of the PHS slab of the CAMP model (Hashimoto et al. 2004) are drawn every 10 km with thin solid lines. The depth data of the CAMP model are extrapolated to the region without data by the “surface” command of GMT, the contours of which are drawn by broken lines. Thick solid lines represent the plate boundaries after Bird (2003). The zone bounded by the dot-and-dash lines is the area that is possibly affected by the tear of the PHS slab, in which the depth contours could be significantly altered. b Depth profile of the PHS slab along each colored line. In the region without depth data, the depth profile follows the extrapolation (broken line). The zone bounded by the dot-and-dash lines shows the area that is possibly affected by the tear of the PHS slab. c Contraction amount of the PHS slab along each colored line as a function of the distance from the western end. In the region without depth data, extrapolated data are used to calculate the contraction amount, which is shown by the broken line