Fault rock heterogeneity produces fault weakness and promotes unstable slip

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Authors

John Bedford, Daniel Faulkner, Nadia Lapusta

Abstract

Geological heterogeneity is abundant in crustal fault zones; however, its role in controlling the mechanical behaviour of faults is poorly constrained. Here, we present laboratory friction experiments on laterally heterogeneous faults, with patches of strong, rate-weakening quartz gouge and weak, rate-strengthening clay gouge. The experiments show that the heterogeneity leads to a significant strength reduction and decrease in frictional stability in comparison to compositionally identical faults with homogeneously mixed gouges typically used in the lab. We identify a combination of weakening effects, including smearing of the weak clay; differential compaction of the two gouges redistributing normal stress; and shear localization producing stress concentrations in the strong quartz patches. The results demonstrate that small-scale geological heterogeneity has pronounced effects on fault strength and stability, and by extension on the occurrence of slow-slip transients versus earthquake ruptures and the characteristics of the resulting events, and should be incorporated in lab experiments, fault friction laws, and earthquake source modelling.

DOI

https://doi.org/10.31223/X51P6W

Subjects

Earth Sciences, Geology, Geophysics and Seismology, Tectonics and Structure

Keywords

Fault

Dates

Published: 2021-08-30 21:06

Last Updated: 2021-08-31 04:06

License

CC BY Attribution 4.0 International

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