Rheological model of the M9 earthquake generating fault. (a) Strength envelope of the thrust fault during interseismic periods (V = 83 mm/year). The frictional and fracture strengths of gabbro (Figure9b) are used for broken and unbroken seamounts. A green arrow indicates a stress drop induced by a collapse of a seamount at the M9 hypocenter. A to C, rupture domains defined by Lay et al. (2012). (b) Velocity dependence of shear strength. The orange line shows the strength envelope of quartz at a faster slip rate (V′ = V × 102). Here τ = 0 and μ = 0.67 are used in the brittle zone, and a-b is defined with a change in steady-state friction coefficient (Δμss) as a - b = Δμss/Δ lnV. The depth of the brittle-ductile transition zone is taken to be 21.5 to 55 km.