Abstract
Despite the hazard posed by earthquakes, we still lack fundamental understanding of the processes that control fault lubrication behind a propagating rupture front and enhance ground acceleration. Laboratory experiments show that fault materials dramatically weaken when sheared at seismic velocities (>0.1 m s−1). Several mechanisms, triggered by shear heating, have been proposed to explain the coseismic weakening of faults, but none of these mechanisms can account for experimental and seismological evidence of weakening. Here we show that, in laboratory experiments, weakening correlates with local temperatures attained during seismic slip in simulated faults for diverse rock-forming minerals. The fault strength evolves according to a simple, material-dependent Arrhenius-type law. Microstructures support this observation by showing the development of a principal slip zone with textures typical of sub-solidus viscous flow. We show evidence that viscous deformation (at either sub- or super-solidus temperatures) is an important, widespread and quantifiable coseismic lubrication process. The operation of these highly effective fault lubrication processes means that more energy is then available for rupture propagation and the radiation of hazardous seismic waves.
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Data availability
The mechanical data used for Figs. 1 and 4 are archived on Zenodo at https://doi.org/10.5281/zenodo.4639947. All data are available from the authors on request. Source data are provided with this paper.
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Acknowledgements
We thank B. Mendis, L. Bowen and F. Barou for their assistance with the acquisition of SEM and TEM images and discussion, and A. Beeby for acquiring Raman spectra on our samples. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 642029 - ITN CREEP to N.D.P. and the Natural Environment Research Council (NERC) through a NERC standard grant NE/H021744/1 to N.D.P.
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G.P. ran the experiments and carried out the microstructural analysis and interpretations. G.P., N.D.P., S.B.N., R.E.H. and T.T. contributed equally to the concept development and to the writing of the paper. All authors jointly supervised this work.
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Supplementary Sections I–VI, Figs. 1–16, Tables 1 and 2, and Equations 1–7.
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Tabulated mechanical data.
Source Data Fig. 4
Tabulated mechanical data.
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Pozzi, G., De Paola, N., Nielsen, S.B. et al. Coseismic fault lubrication by viscous deformation. Nat. Geosci. 14, 437–442 (2021). https://doi.org/10.1038/s41561-021-00747-8
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DOI: https://doi.org/10.1038/s41561-021-00747-8
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