Unlocking the effects of friction on fault damage zones

Two-dimensional, numerical models of a linear fault embedded within a linear elastic medium show the generation of off-fault tensile failure that results from inelastic slip along the fault. We explore quasi-static models with slip-weakening friction to assess the effects of spatially and temporally variable friction on the damage patterns. Tensile fractures form where tangential normal stresses along the fault exceed the tensile strength of the rock. These stresses result from locally high slip gradients at the rupture tip. Because faults of different displacement history and rock type could have varying slip-weakening distances, we examine the effect of changing the slip-weakening distance on the damage pattern and find that this parameter is important in determining off-fault fracture intensity and continuity along strike. Faults with short slip-weakening distance produce greater off-fault damage and significantly greater seismic radiated energy than faults with longer slip-weakening distances. We also investigate the effect of pre-existing damage on the subsequent development of fractures in second generation slip episodes and find that damage localizes onto pre-existing patches. These results could guide field studies of small faults as to whether the fault failed in one slip event or multiple small events.