Improved rheological model of the Tohoku-oki megathrust. Here the ‘simple’ rheological profile in Figure7 is modified using the pore pressure model shown in Figure6 and considering the brittle-ductile transitional behaviors of quartz and gabbro. (a) Depth-dependent changes in model parameters, μ∗, and α. Brittle-ductile transitional behaviors of gabbro and quartz are taken into account in purple and thick pink lines, respectively. (b) Shear strength along the interplate megathrust. The fracture and frictional strengths (shown as green and orange lines, respectively) of gabbro and siliceous rocks were calculated assuming λ = 0.53. The strength envelopes of quartz and gabbroic rocks are shown as thick pink and purple lines, respectively.