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Book Sections Year : 2012

Shear localization in deep geological layers during seismic slip

Jean Sulem
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It is well known that strain localization during seismic slip occurs as the result of a plastic instability. A key parameter in the analysis of dynamic slip and weakening of the shear stress is the actual thickness of the zone of localized deformation. In the first part of this chapter, we analyse the stability of undrained adiabatic shearing of a saturated rock layer. This corresponds to the situation when the slip event is sufficiently rapid and the shear zone broad enough to effectively preclude heat or fluid transfer as in the case of an earthquake or a landslide. The kinetics of the fault gouge inside the sheared rock layer is described by a Cosserat continuum, and we incorporate the effect of shear heating due to the dissipation of the frictional work. It is shown that shear heating has a destabilizing effect and that instability can occur in the hardening regime of the stress-strain curve if the amount of dilatant strengthening is not sufficient as compared to the effect of thermal pressurization of the pore fluid. It is shown that the linear stability analysis with macro and micro-inertia terms leads to the selection of a preferred wavelength of the instability mode corresponding to the instability mode with fastest (but finite) growth coefficient. The selected wavelength is compatible with observed shear-band thickness in fault zones. In the second part of the chapter, we analyse the effect of temperature-induced decomposition of minerals and show how thermal pressurization of the pore fluid and thermal decomposition of minerals induced by shear heating limit the co-seismic temperature rise, which may explain the lack of pronounced heat outflow and the lack of shallow frictional melting, along major tectonic faults.
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hal-00952147 , version 1 (26-02-2014)



Jean Sulem. Shear localization in deep geological layers during seismic slip. B. Dodd and Bai (Eds). Adiabatic shear localization, Frontiers and advances, 2nd ed., pp.397-423, 2012, ⟨10.1016/B978-0-08-097781-2.00010-1⟩. ⟨hal-00952147⟩
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