Dilatancy Toughening of Shear Cracks and Implications for Slow Rupture Propagation

Dilatancy associated with fault slip produces a transient pore pressure drop which increases frictional strength. This effect is analysed in steadily propagating rupture model that includes weakening, slip-dependent dilation and fluid flow. shown to increase the stress intensity factor required propagate tip. With increasing speed, an undrained (strengthened) region develops near tip extends beyond frictionally weakened zone. Away from region, diffusion gradually recharges strength returns drained, value. For sufficiently large dimensions, dilation-induced equivalent toughness proportional square root of speed. In general, has for growth by decreasing along crack. Thermal pressurisation potential compensate dilatant strengthening effect, at expense increased heating rate, might lead premature melting. Using reasonable laboratory parameters, dilatancy-toughening leads dynamics quantitatively consistent observed slow events subduction zones.