The spectrum of fault slip in elastoplastic fault zones

Creators: Mia, Md Shumon¹; Abdelmeguid, Mohamed^{1, 2}; Elbanna, Ahmed E.¹

1. University of Illinois Urbana-Champaign
2. California Institute of Technology

Abstract

Natural faults are typically surrounded by damage zones that exhibit inelastic material response. This study investigates the role of fault zone strength in modulating the spectrum of fault slip across different spatio-temporal scales. We carry out long-term simulations of seismic and aseismic slip for an elastoplastic spring slider model with rate-and-state friction as well as a continuum model of a 2D anti-plane rate-and-state fault embedded in an elastoplastic bulk. Results of the elastoplastic spring slider model show the emergence of a new stability boundary, depending on the bulk yield strength relative to fault frictional strength, that limits the rupture size regardless of the fault length. Continuum simulations generate a spectrum of slip analogous to the spring slider model including localized or migrating events of slow and fast slip. A fault may remain locked for yield strength sufficiently low and close to fault reference strength even if it is intrinsically rate weakening and larger than the nucleation length scale predicted by the elastic analysis. These findings shed new light on the nature of fault frictional stability and suggest the critical role of the fault zone rheological properties in modulating the spectrum of fault slip.

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Acknowledgement

The authors acknowledge support from the Southern California Earthquake Center through a collaborative agreement between NSF, Grant Number: EAR0529922 and USGS, Grant Number: 07HQAG0008 and the National Science Foundation CAREER award No. 1753249 for modeling complex fault zone structures. This material is also based upon work partially supported by the Department of Energy under Award Number DE-FE0031685 to investigate spatio-temporal complexity of induced earthquakes. The authors are also grateful for the insightful comments from two anonymous reviewers, which helped improve the manuscript.

Contributions

Md Shumon Mia: Conceptualization, Formal analysis, Methodology, Software, Visualization, Writing – original draft, Writing – review & editing. Mohamed Abdelmeguid: Conceptualization, Formal analysis, Methodology, Software, Visualization, Writing – review & editing. Ahmed E. Elbanna: Conceptualization, Formal analysis, Funding acquisition, Methodology, Software, Supervision, Visualization, Writing – original draft, Writing – review & editing.

Data Availability

Data generated from the numerical simulations are uploaded on an open access repository (https://doi.org/10.5281/zenodo.7718768).

Supplemental Material

The Supplementary Information includes: • Text S1 outlines the frictional law. • Text S2 outlines the elastoplastic spring slider model. • Text S3 outlines the model setup and methods. • Table S1 provides input parameters for the simulations. • Figure S1 shows schematic of fault zone and elastoplastic spring slider model. • Figure S2 shows model geometry and hybrid scheme setup. • Figure S3 shows results of fully dynamics simulations for yield strength 33.5 MPa, 36 MPa and elastic case. Slip patterns are qualitatively similar to the quasi-dynamics cases presented in the main text. • Figure S4 shows spatial extent of off-fault plasticity for yield strength 31 MPa and 33.5 MPa. (PDF)

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