Effect of water and confining pressure on fault slip behaviors and rupture propagation

Pore fluid is ubiquitous within the Earth's crust and severely impacts shear rupture propagation and the slip behaviors of faults. We conducted triaxial experiments on sandstone to investigate the effects of crack damage, confining pressure, and water on fault slip behaviors and rupture propagation. Two loading configurations, conventional loading and increasing-amplitude cyclic loading, were conducted to compare the inelastic behavior and failure modes of sandstone samples. In addition to a macroscopic deformation and mechanical properties analysis, a noncontact optical scanner and magnetic resonance imaging technique were used to analyze the microstructural evolution of the sandstone. The results show that a higher confining pressure results in a more homogeneous fault plane. Fault slip behaviors can be divided into the slip-strengthening and slip-weakening stages. In the brittle regime, pore water reduces the brittle strength of rocks but does not induce different fault slip behaviors. When the confinement is high enough, rocks fail in the brittle–ductile transition regime where dynamic faulting is prohibited. In the brittle–ductile transitional regime, pore water enhances stabilization, and the slip behaviors distinctively differ from those occurring without water.