Modeling Sequence of Earthquakes and Aseismic Slip With High Resolution Fault Zone Physics

Abstract:

We present FEBI: a novel hybrid finite element (FE) - spectral boundary integral (SBI) scheme that enables efficient simulation of sequence of earthquakes and aseismic slip. This combined FE-SBI approach captures the benefits of finite elements in modelling problems with nonlinearities, as well as the computational superiority of SBI. The domain truncation enabled by this scheme allows us to utilize high-resolution finite elements discretization to capture inhomogeneities or complexities that may exist in a narrow region surrounding the fault. Combined with an adaptive time stepping algorithm, this framework opens new opportunities for modeling earthquake cycles with high-resolution fault zone physics. In this talk, we consider a two dimensional (2-D) anti-plane model with a vertical strike-slip fault governed by rate and state friction. Aseismic slip is modeled using an implicit quasi-dynamic formulation with the radiation damping approximation. Rapid seismic slip is modeled using an explicit fully dynamic procedure. The proposed approach is verified using the benchmark problem BP-3 from the Southern California Earthquake Center (SCEC) sequence of earthquake and aseismic slip (SEAS) community verification effort. The computational framework is then utilized to model the earthquake sequence and aseismic slip of a fault embedded within a low-velocity fault zone (LVFZ) with different widths and compliance levels. Our results indicate that sufficiently compliant LVFZs contribute to the emergence of sub-surface events that fail to penetrate to the free surface and may experience earthquake clusters with nonuniform inter-seismic time. Furthermore, the LVFZ leads to slip rate amplification relative to the homogeneous elastic case and persistence of slip pulse like ruptures. We discuss the implications of our results for understanding earthquake complexity as an interplay of fault friction and bulk heterogeneities.