Fault rock heterogeneity produces fault weakness and promotes unstable slip

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John Bedford, Daniel Faulkner, Nadia Lapusta


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.




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




Published: 2021-08-30 21:06

Last Updated: 2021-08-31 04:06


CC BY Attribution 4.0 International

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