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Scale dependence of earthquake rupture prestress in models with enhanced weakening: implications for event statistics and inferences of fault stress

Lambert, Valère and Lapusta, Nadia and Faulkner, Daniel (2021) Scale dependence of earthquake rupture prestress in models with enhanced weakening: implications for event statistics and inferences of fault stress. . (Unpublished)

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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 1) illustrate that large earthquakes can occur on faults that appear not to be critically stressed compared to stresses required for slip nucleation; 2) highlight the importance of finite-fault modeling in relating the local friction behavior determined in the lab to the field scale; and 3) 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.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Lambert, Valère0000-0002-6174-9651
Lapusta, Nadia0000-0001-6558-0323
Faulkner, Daniel0000-0002-6750-3775
Additional Information:The copyright holder for this preprint is the author/funder. Published Online: Tue, 16 Feb 2021. This study was supported by the National Science Foundation (grants EAR 1724686) and the Southern California Earthquake Center (SCEC), contribution No. 10782. SCEC is funded by NSF Cooperative Agreement EAR-1033462 and USGS Cooperative Agreement G12AC20038. D. Faulkner was supported by the Natural Environment Research Council (grants NE/P002943/1 and NE/R017484/1). The numerical simulations for this work were done on the High Performance Computing Central cluster of the California Institute of Technology. The data supporting the analysis and conclusions is given in Figures and Tables, in the main text and supplementary materials. Data is accessible through the CaltechDATA repository ( We thank Tom Heaton, Hiroo Kanamori, and Emily Brodsky for helpful discussions.
Group:Seismological Laboratory
Funding AgencyGrant Number
Natural Environment Research Council (NERC)NE/P002943/1
Natural Environment Research Council (NERC)NE/R017484/1
Subject Keywords:Geophysics / Seismology and Seismic Exploration, Geophysics / Solid-Earth and Geophysics, Geophysics / Tectonics, Geophysics, Geophysics / Heat Flow
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Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center10782
Record Number:CaltechAUTHORS:20210216-124009098
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108068
Deposited By: Tony Diaz
Deposited On:16 Feb 2021 21:16
Last Modified:16 Feb 2021 21:16

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