Steady Propagation of Plane Strain Shear Cracks on an Impermeable Plane in an Elastic Diffusive Solid

Quasi-static shear crack propagation in a linear elastic fluid-saturated porous solid c;Iuses a change of pore pressure on the crack plane if it is impermeable but not if it is permeable. Assuming that the pore pressure induced on the crack plane reduces the efTcclive compressive stress (total stress minus pore fluid pressure) and. as a result. the frictional resistance. we find that the energy required to drive the crack is decreased by up to about 60% of the value required in a purely elastic solid. The required energy decreases with velocity at low and high velocities. but increases with velocity for C’//c in the range of IO” ‘-IO’. where c’is the speed of propagation, I is the loodcd length of the semi-infinite crack and c is the diffusivity. When the erect of the pore prcssurc induced on the crack plane is neglected. the results are quahtatively similar lo those of Rice and Simons (1976. 1. Gcvplr,u. Rcs. RI. 53 2?-SNJ) for the permeable crack: coupling bctwcwn dcformarion and _ dilrusion stabilizes propapalion in the sense that the energy that must bc supplied to drive rhc crack incrcascs with velocity within a tinitc range of the ratio 27/c. This range of I’/ c is about an order of magnitude lower than Ihat for the permcahlc crack. hut includes fhc range cited above and is wlthin the range of ohscrvcd creep events on the San Andrcas faull.