Evolving geometrical and material properties of fault zones in a damage rheology model

We discuss numerical simulations of evolving fault zone structures in a 3-D lithospheric model with a seismogenic crust governed by a damage rheology that accounts for large strain associated with permanent brittle deformation. Results for the initial propagation of an existing narrow damage zone subjected to oblique loading exhibit strong asymmetry of the evolving damage with respect to the initial fault orientation and predict out-of-plane directions of the propagating damage zones. The orientations of the simulated damage zones agree with analytical expectations based on fracture mechanics for the directions of wing cracks generated at the tips of a crack under mixed mode loading. Lithosphere-scale numerical simulations for the long-term evolution of a large strike-slip fault zone produce initially a system of stepping en echelon segments associated with the asymmetric generation of new damage zones. The simulated fault zone segments evolve with continuing deformation to a throughgoing localized structure. Large-scale perturbation in the geometry of the Moho interface together with the regional heat regime can reduce considerably the degree of localization of the fault zone structure and the associated deformation fields.