| Summary: | Different physical processes associated with material failure affect earthquake rupture nucleation and propagation. These processes are frictional sliding along faults of different roughness, fracturing of the intact rock sections connecting the preexisting planes of weakness (fault step overs) or cemented fault segments, fault branching and "wing-crack" formation, inelastic deformation in the fault damage zone, and others. Due to the computational complexity of earthquake models, especially if complex fault geometries and heterogeneity of properties are also considered, all of these failure related processes are usually combined into their simplified mathematical representations: the failure law prescribed along the fault and the bulk rheology.
In this work we explore both aspects. We study the effect of different failure parameterizations on the earthquake cycle characteristics, earthquake nucleation and dynamic rupture propagation. We start with simplified spring-slider models to understand the stability, slip regimes, and characteristics of the different phases of the earthquake cycle with different failure laws for the case of a single degree of freedom dynamic system. We then perform 2D finite element models of earthquake rupture nucleation and propagation to gain insight into how different failure laws affect the different phases of the earthquake cycle in the case of an added fault dimension. The rheological part of this work explores the effect of off-fault plastic deformation on elongated earthquake rupture characteristics, their steady-state velocity and energy balance. We use a 2.5D spectral element method that approximately accounts for 3D effects while modeling a 2D geometry and explore the dependence of earthquake rupture risetime, steady state slip rate and speed, plastic energy release rate etc. on the initial stress state and plastic properties of the bulk material.
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