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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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Strong asperities nucleate earthquakes on laboratory faults
Abundant heterogeneity has been documented on faults in nature across a wide range of length scales, including structural, mineralogical, and roughness variations. The role of complex heterogeneity on fault mechanics and frictional stability is not well established, and experiments investigating heterogeneity have typically incorporated a single source of heterogeneity. Here, we conduct rock friction experiments on rough, bimaterial faults that are creeping, or steadily sliding, to explore the role of lithological heterogeneity on fault mechanics and stability. When strong asperities juxtapose weak gouge, stable sliding occurs with a low friction coefficient, µ. Encounters of strong diabase asperities on talc gouge lined faults initiate dramatic increases in µ and transitions to unstable sliding characterized by frequent stick-slip events (StSE). Seismic moments and stress drops of StSE decrease with increasing asperity abundance. Stress is concentrated at asperities during encounters, increasing with decreasing asperity abundance and leading to extensive mechanical damage. Interactions between strong, velocity weakening asperities provide a model to explain the nucleation of seismic and aseismic slip events on nominally stable, creeping faults.
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- Award ID(s):
- 2052897
- PAR ID:
- 10596188
- Publisher / Repository:
- Geology
- Date Published:
- Journal Name:
- Geology
- Volume:
- 53
- Issue:
- 5
- ISSN:
- 0091-7613
- Page Range / eLocation ID:
- 420 to 424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1130/g52853.1
