Dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk

We discuss 2D simulations of in-plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault. The fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress, while plastic strain in the bulk is governed by a Coulomb yielding criterion. The occurrence of off-fault damage stabilizes the slip velocity on the fault. Stable self-sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault. Plastic strain is generated only on the stiffer side of the fault (the tensional quadrant in the direction of rupture propagation) in a strip of approximately constant width that is correlated with the slip velocity on the fault. Simulations for various values of confining normal stress, material contrast and cohesion in the bulk suggest that significant generation of off-fault damage is limited to conditions that correspond to the top few kilometers of the crust. The results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults.