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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 reduction in strength and frictional stability in comparison to compositionally identical faults with homogeneously mixed gouges. 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 geological heterogeneity and its evolution can have 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 further studied in lab experiments and earthquake source modelling.
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Apparent Age Dependence of the Fault Weakening Distance in Rock Friction
Abstract During rock friction experiments at large displacement, room temperature and humidity, and following a hold test, the fracture energy increases approximately as the square of the logarithm of hold duration. While it's been long known that failure strength increases with log hold time, here the slip weakening distance,dh, also increases. The weakening distance increase is large, hundreds of percent change over a few thousand seconds. The initial bare surface and simulated fault gouge experiments were conducted in rotary shear at 25 MPa normal stress, 21 MPa confining stress and at displacements greater than 100 mm. In contrast, initially bare surface experiments at 5 MPa normal stress, unconfined at displacements less than 10 mm show effectively no change indh. We attribute the difference to the presence of an appreciable shear zone that develops due to wear over significant displacements, confined at elevated normal stress. Prior published studies of sheared simulated fault gouge at short displacement show both acknowledged and unacknowledged increases indhthat may relate to our observations. Since natural faults have well‐developed shear zones, the observations have more direct relevance to earthquake nucleation than prior laboratory studies that use short displacement data and focus on frictional strength recovery alone. However, the physics underlying this increase in weakening distance are not known; candidates are compaction (Nakatani, 1998) and delocalization (Sleep et al., 2000). Additional caveats are that these are room temperature and humidity experiments, at a single normal stress that have not yet been reproduced in other laboratories.
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- Award ID(s):
- 2054439
- PAR ID:
- 10364123
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 127
- Issue:
- 1
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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