Modeling Sequence of Earthquakes and Aseismic Slip (SEAS) in Complex Faults Zones Using a Computationally Efficient Numerical Algorithm

Modeling earthquake ruptures is a complex challenge due to the eclectic sources of nonlinearities and heterogeneities, such as friction, plasticity, nonplanar fault surfaces, and material damage. In addition to the nonlinearities, another challenging aspect of modeling earthquake processes is the multi-scale nature of the problem, both spatially and temporally. Here, we present a hybrid scheme that combines finite element method (FEM) and spectral boundary integral method (SBIM) to simulate earthquake cycles with rate and state fault subjected to slow tectonic loading processes of long duration intermittent by episodes of dynamic fracture in the presence of near-field heterogeneity. On a spatial level, regions of small-scale heterogeneity and complex fault geometry are handled using a FEM approach, while the linearly elastic bulk with a known Greens function is modeled using SBIM. Accordingly, we benefit from the flexibility of FEM in handling nonlinear problems, while retaining the superior performance and accuracy of SBIM. We handle the intricacies associated with this time evolution using an alternating dynamic-quasidynamic schemes, such that during dynamic rupture an explicit time integration is utilized for computational efficiency, with the quasidynamic approximation being specific only to inter-seismic periods where larger time steps are required. The presented approach is validated using benchmark problems. We further demonstrate the capabilities of this computationally efficient scheme by modeling earthquake cycles with LVFZ and various fault zone complexities, in which we highlight the role of near fault nonlinearities in altering the behavior of the earthquake cycle including interevent time, magnitude scaling, peak slip rate, and radiation pattern.