Off-fault inelastic deformation and orientations of microcracks induced by dynamic ruptures on a 3D strike-slip fault with a bend

Large dynamic stress associated with an earthquake rupture may exceed the yielding strength of the surrounding rock. It leads to irrecoverable deformation off the fault. When a fault geometrical complexity is present, it induces stress heterogeneity that may further promote the development of off-fault inelastic deformation. Analyses of the inelastic strain induced by a dynamic rupture help understand the evolution of a fault system and its surrounding rock. In this study, we simulate dynamic ruptures governed by the slip-weakening law on a 3D strike-slip fault with a bend of 15˚. A depth-dependent regional stress is applied, and the rock may yield based on the Drucker-Prager criterion. The plastic deformation in our models resembles shear microcracks and damage of rocks associated with dynamic ruptures. The inelastic strain tensors are presented in the form of beach balls, whose nodal planes represent the maximum inelastic shear strain. The orientations of shear microcracks are about 15˚ from the nodal planes. We focus on the inelastic strain distributions and orientations near the fault bend. Major results are as below. 1) The inelastic strain is widely distributed at shallow depth but is distributed narrowly near the fault at deep depth. 2) The inelastic strain is more widely distributed and has larger magnitude on the dilatational side of the bend compared to that on the compressional side. 3) At the shallow 100 m depth, the shear microcracks induced by the dynamic rupture orient at shallow dip angles on the dilatational side of the bend, while orient at high dip angles on the compressional side of the bend. 4) At 1100 m depth, the inelastic strain that is larger than 0.0001 mainly exists on the dilatational side of the bend and the orientations of microcracks have shallow dip angles. 5) At 3100 m and deeper, the inelastic strain that is larger than 0.0001 only exists on the dilatational side of one fault segment. Putting in a larger context of earthquake cycles, the inelastic strain may have profound effects on the long-term dynamical response of a geometrically complex fault. Our study helps understand features of shear microcracks induced by dynamic ruptures and a fault complex geometry, and their implications for future earthquakes.