Letter | Published:

Fault weakening and earthquake instability by powder lubrication

Nature volume 467, pages 452455 (23 September 2010) | Download Citation

Abstract

Earthquake instability has long been attributed to fault weakening during accelerated slip1, and a central question of earthquake physics is identifying the mechanisms that control this weakening2. Even with much experimental effort2,3,4,5,6,7,8,9,10,11,12, the weakening mechanisms have remained enigmatic. Here we present evidence for dynamic weakening of experimental faults that are sheared at velocities approaching earthquake slip rates. The experimental faults, which were made of room-dry, solid granite blocks, quickly wore to form a fine-grain rock powder known as gouge. At modest slip velocities of 10–60 mm s−1, this newly formed gouge organized itself into a thin deforming layer that reduced the fault’s strength by a factor of 2–3. After slip, the gouge rapidly ‘aged’ and the fault regained its strength in a matter of hours to days. Therefore, only newly formed gouge can weaken the experimental faults. Dynamic gouge formation is expected to be a common and effective mechanism of earthquake instability in the brittle crust as (1) gouge always forms during fault slip5,10,12,13,14,15,16,17,18,19,20; (2) fault-gouge behaves similarly to industrial powder lubricants21; (3) dynamic gouge formation explains various significant earthquake properties; and (4) gouge lubricant can form for a wide range of fault configurations, compositions and temperatures15.

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Acknowledgements

We thank J. Young, who built our instrument, as well as E. Eshkol, M. Hamilton, D. Moore, A. Madden, J. Chang and S. Busetti. Comments and reviews by J. Andrews, N. Beeler, C. Sammis, T.-f. Wong and J. Fineberg improved the manuscript. This study is supported by the National Science Foundation, Geosciences, Equipment and Facilities (grant number 0732715).

Author information

Affiliations

  1. School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma, USA

    • Ze’ev Reches
  2. US Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA

    • David A. Lockner

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Contributions

All authors made equal contributions to this study.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Ze’ev Reches or David A. Lockner.

Supplementary information

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  1. 1.

    Supplementary Information

    This file contains Supplementary Information comprising Experimental set- up, Steady-state friction and Wear calculation. Also included are and Supplementary Figures 1-6 with legends and an additional reference.

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https://doi.org/10.1038/nature09348

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