Model space for the two-dimensional numerical simulation of the thermal structure. The model space is 800-km long by 400-km deep. The geometry of the subducted plate is set manually, and the subduction velocity (convergence rate) is given in that region. The oceanic plate initiates subduction at the beginning of the calculation and then continues to subduct deeper as time proceeds. The plate thickness is set at 80 km. The continental crust is set from the surface to a depth of 32 km, below which rigid mantle is set down to a depth of 70 km. The red line represents the location on the plate interface where shear heating is applied. The boundary conditions are written at each boundary with blue characters. The grid size for temperature (T) and flow function (ψ) used in the calculation is also shown.