Fig. 5

Model results showing the horizontal velocity and shear rate and shear rate gradient in the centre of the subduction zone below the base of the overriding plate at 31.7 and 182.6 Myr. a, e Location of line at ~150 km below the base of the overriding plate, with colour scheme in overriding plate indicating trench-normal horizontal deviatoric normal stress (σ _XX). b, f Horizontal trench-normal velocity in the mantle (v _x ) at ~150 km below the base of the overriding plate (continuous line) and in the overriding plate (dashed line). Note that the direction towards the right (in the positive x-direction) is taken as positive. c, g Average horizontal trench-normal shear rate (dv _x /dy) in a ~150 km thick mantle section below the base of the overriding plate. Note that a basal drag in the direction towards the right (in the positive x-direction) is positive. d, h Trench-normal horizontal gradient of the average horizontal trench-normal shear rate (d(dv _x /dy)/dx) in a ~150 km thick mantle section below the base of the overriding plate. Note that a positive gradient induces trench-normal overriding plate extension, while a negative gradient induces trench-normal overriding plate shortening. The pale red zone in d for 31.7 Myr indicates a zone with a strong positive gradient, while the pale blue zones in h for 182.6 Myr indicate zones with a strong negative gradient