Modeling the earthquake cycle with heterogeneous materials and off-fault plasticity

Brittany Erickson

Portland State University

Date & Time
Building 3, Rambo Auditorium
Josie Nevitt

Current models for dynamic rupture have led to much insight into earthquake propagation, the generation of high-frequency ground motion, and the influence of plasticity on rupture propagation. Although the inclusion of a plastic material response has been shown to reduce stress and slip velocities at the rupture front to reasonable values, little work has been done to understand the evolution of a damage zone (and its impact on rupture) over multiple event sequences. In particular, most dynamic rupture models currently make the assumption of a uniform background stress and are limited to single-event simulations. In this talk I will share the method we have developed for earthquake cycle simulations within heterogeneous, inelastic material, where ruptures nucleate under self-consistent initial conditions. The method is developed for the classical antiplane problem of a vertical strike-slip fault governed by rate-and-state friction, with inertial effects captured through the radiation-damping approximation. Both rate-independent plasticity and viscoplasticity are considered, where stresses are constrained by a Drucker-Prager yield condition. The off-fault volume is discretized using finite differences and tectonic loading is imposed by displacing the remote side boundaries at a constant rate. We quantify how viscosity, isotropic hardening, and cohesion affect the magnitude and off-fault extent of plastic strain that develops over many ruptures. In all cases, coseismic slip in the shallow sub-surface is diminished compared to slip accumulated at depth during interseismic loading. The evolution of this slip deficit with each subsequent event, however, is dictated by the plasticity model. Integration of the off-fault plastic strain from the viscoplastic model reveals that a significant amount of tectonic offset is accommodated by inelastic deformation (about 10% of the tectonic deformation budget).

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