Dynamic rupture propagation on fault planes with explicit representation of short branches

Abstract

An active fault zone is home to a plethora of complex structural and geometric features that are expected to affect earthquake rupture nucleation, propagation, and arrest, as well as interseismic deformation. Simulations of these complexities have been largely done using continuum plasticity or scalar damage theories. In this paper, we use a highly efficient novel hybrid finite element-spectral boundary integral equation scheme to investigate the dynamics of fault zones with small scale pre-existing branches as a first step towards explicit representation of anisotropic damage features in fault zones. The hybrid computational scheme enables exact near-field truncation of the elastodynamic field allowing us to use high resolution finite element discretization in a narrow region surrounding the fault zone that encompasses the small scale branches while remaining computationally efficient. Our results suggest that the small scale branches may influence the rupture in ways that may not be realizable in homogenized continuum models. Specifically, we show that these short secondary branches significantly affect the post event stress state on the main fault leading to strong heterogeneities in both normal and shear stresses and also contribute to the enhanced generation of high frequency radiation. The secondary branches also affect off-fault plastic strain distribution and suggest that co-seismic inelasticity is sensitive to pre-existing damage features. We discuss our results in the larger context of the need for modeling earthquake ruptures with high resolution fault zone physics.

Earthquake Source Complexity Controls the Frequency Dependence of Near‐Source Radiation Patterns

“…This may be because directivity effects, while prominent at low frequencies, are often not preserved in the frequency bands we consider in this study (Pacor et al, 2016;Somerville et al, 1997). In summary, earthquake rupture dynamics can be sensitive to various forms of fault zone complexity (Huang & Ampuero, 2011;Huang et al, 2014;Ma & Elbanna, 2019), which in turn can influence the details of the recorded seismic wavefield (Ben-Zion & Ampuero, 2009;Trugman et al, 2020;Tsai & Hirth, 2020;Tsai et al, 2021).…”

Crack to pulse transition and magnitude statistics during earthquake cycles on a self-similar rough fault

“…Dunham et al, 2011b,a;Shi and Day, 2013). However, such continuum plasticity models may not be able to accurately represent an important source of relaxation that occurs off the main fault on discrete structures such as fault branches (Ma and Elbanna, 2019). Further developments of earthquake cycle simulations are needed before we can efficiently simulate multiple cycles on rough faults with realistic stress relaxation mechanisms; in the meantime, backslip offers a simple way to investigate these problems.…”

The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)

“…Robust predictive models of earthquake source processes have become important means for studying fundamental questions in earthquake science. Models of single earthquakes (known as dynamic rupture simulations) have emerged as powerful tools for understanding the influence of fault geometry, friction and prestress on rupture propagation, and for explaining observations of high-frequency ground motions and damage zones (Day, 1982;Olsen et al, 1997;Nielsen et al, 2000;Duan and Oglesby, 2006;Ripperger et al, 2007;Bhat et al, 2007;Dunham et al, 2011a,b;Lozos et al, 2011;Gabriel et al, 2012;Shi and Day, 2013;Kozdon and Dunham, 2013;Xu et al, 2015;Wollherr et al, 2018;Ma and Elbanna, 2019). Many of the codes used for these studies incorporate advanced features such as 3D domains and complex fault geometries, leading to very large problems for which rigorous convergence tests can be too computationally expensive.…”