A Novel Hybrid Finite Element-Spectral Boundary Integral 1 Scheme for Modeling Earthquake Cycles : Application to 2 Rate and State Faults with Low-Velocity Zones

Abstract

12 We present a novel hybrid finite element (FE) spectral boundary integral (SBI) scheme 13 that enables efficient simulation of the slip evolution on faults, with near-field heterogeneities 14 or nonlinearities, subjected to slow tectonic loading processes with episodes of spontaneously 15 occurring events. This combined FE-SBI approach captures the benefits of finite elements in 16 modelling problems with nonlinearities, as well as the computational superiority of SBI. The 17 domain truncation enabled by this scheme allows us to utilize high-resolution finite elements 18 discretization to capture inhomogeneities or complexities that may exist in a narrow region sur19 rounding the fault. Combined with an adaptive time stepping algorithm, this framework opens 20 new opportunities for modeling earthquake cycles with high-resolution fault zone physics. In 21 this initial study, we consider a two dimensional (2-D) anti-plane model with a vertical strike22 slip fault governed by rate and state friction. The proposed approach is first verified using the 23 benchmark problem BP-1 from the SCEC SEAS repository. The computational framework is 24 then utilized to model the earthquake sequence and aseismic slip of a fault embedded within 25 a low-velocity fault zone (LVFZ) with different widths and compliance levels. Our results in26 dicate that sufficiently compliant LVFZs contribute to the emergence of sub-surface events that 27 fail to penetrate to the free surface and may experience earthquake clusters with nonuniform 28 inter-seismic time. Furthermore, the LVFZ leads to slip rate amplification relative to the ho29 mogeneous elastic case. We discuss the implications of our results for understanding earthquake 30 complexity as an interplay of fault friction and bulk heterogeneities. 31