Fig. 2

Calculation procedure. a Initial conditions. b Distinction between oceanic crust and upper mantle is removed at > 150 km depth. c When the slab tip reaches a depth of 250 km, (1) area of mantle wedge (bounded by the slab surface, a horizontal range between the location of the slab surface at depths of 80–200 km and depths z > 30 km) is replaced by materials with lower viscosity and density, and (2) the frictional properties for mantle and crust above the mantle wedge are decreased to c = 1 MPa and ϕ = ϕ _AL. After this time, (3) the depth where oceanic crust is no longer distinguished from mantle is changed to 100 km, and (4) the subducting plate is free to move in response to the underlying dynamics. d Geometry of the mantle wedge changes according to the calculated slab geometry. A red circle indicates the position of the marker used to measure trench velocity (V_tr)