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Caractérisation expérimentale du frottement effectif des zones de faille

Abstract : We present a series of experimental results aiming at modeling the mechanical behavior of fault zones. We employed an annular simple shear apparatus allowing to apply plurimetric shear displacements to thick granular gouge samples (quartz sand). Our results evidence a new, spectacular slip-weakening process: the effective coefficient of friction of the gouge drops by about 70% over decimetric slip distances. This friction decrease with imposed slip is very well modeled by a power law, thus not featuring any characteristic length scale. Furthermore, and for the first time in an experimental study, the apparent weakening distance as well as the rupture energy involved in this new slip-weakening process appear in good quantitative agreement with those estimated for large earthquakes. We propose to include this slip-weakening into an extension of the classical rate- and state-dependent friction laws. Besides these mechanical measurements, an image correlation technique also enabled us to monitor the microscopic deformations inside the samples during the runs. We observe that, soon after the onset of slip, the deformation localizes inside a comminuted shear band whose thickness remains remarkably constant with ongoing shear. This shear band is separated from the rest of the sample by a thin and indurated transition layer. We also report that the macroscopic slip-weakening process is systematically associated, outside of the shear band, to a slow relaxation of the local strain increments. We interpret both the micro- and the macro-relaxations as resulting from a progressive decoupling between the shear band and the bulk of the sample. The mechanical, effective thickness of the gouge samples thus appears significantly larger than the thickness of the shear band alone. We propose to extrapolate our mechanical and microscopic results to real fault zones, whose structure frequently presents strong analogies with that of our sheared samples.
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Contributor : Guillaume Chambon <>
Submitted on : Friday, July 30, 2004 - 12:14:22 PM
Last modification on : Thursday, October 29, 2020 - 3:01:24 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:29:53 PM

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Guillaume Chambon. Caractérisation expérimentale du frottement effectif des zones de faille. Géologie appliquée. Université Paris Sud - Paris XI, 2003. Français. ⟨tel-00006613⟩

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