Scale Dependence of Earthquake Rupture Prestress in Models With Enhanced Weakening: Implications for Event Statistics and Inferences of Fault Stress

Lambert, Valère ORCID: 0000-0002-6174-9651, Lapusta, Nadia ORCID: 0000-0001-6558-0323 and Faulkner, Daniel ORCID: 0000-0002-6750-3775 (2021) Scale Dependence of Earthquake Rupture Prestress in Models With Enhanced Weakening: Implications for Event Statistics and Inferences of Fault Stress. Journal of Geophysical Research: Solid Earth, 126 (10).

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Official URL: http://dx.doi.org/10.1029/2021jb021886

Abstract

<jats:title>Abstract</jats:title><jats:p>Determining conditions for earthquake slip on faults is a key goal of fault mechanics highly relevant to seismic hazard. Previous studies have demonstrated that enhanced dynamic weakening (EDW) can lead to dynamic rupture of faults with much lower shear stress than required for rupture nucleation. We study the stress conditions before earthquake ruptures of different sizes that spontaneously evolve in numerical simulations of earthquake sequences on rate‐and‐state faults with EDW due to thermal pressurization of pore fluids. We find that average shear stress right before dynamic rupture (aka shear prestress) systematically varies with the rupture size. The smallest ruptures have prestress comparable to the local shear stress required for nucleation. Larger ruptures weaken the fault more, propagate over increasingly under‐stressed areas due to dynamic stress concentration, and result in progressively lower average prestress over the entire rupture. The effect is more significant in fault models with more efficient EDW. We find that, as a result, fault models with more efficient weakening produce fewer small events and result in systematically lower b‐values of the frequency‐magnitude event distributions. The findings (a) illustrate that large earthquakes can occur on faults that appear not to be critically stressed compared to stresses required for slip nucleation; (b) highlight the importance of finite‐fault modeling in relating the local friction behavior determined in the lab to the field scale; and (c) suggest that paucity of small events or seismic quiescence may be the observational indication of mature faults that operate under low shear stress due to EDW.</jats:p>

Item Type:	Article
Divisions:	Faculty of Science and Engineering > School of Environmental Sciences
Depositing User:	Symplectic Admin
Date Deposited:	21 Dec 2021 13:47
Last Modified:	04 Sep 2023 03:04
DOI:	10.1029/2021jb021886
Open Access URL:	https://agupubs.onlinelibrary.wiley.com/doi/10.102...
Related URLs:	Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3145779