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SLIP-WEAKENING MECHANISMS AT HIGH SLIP-VELOCITIES: INSIGHTS FROM ANALOGUE AND NUMERICAL MODELLINGS

Abstract : This thesis aims at studying the thermo-poro-mechanical properties of fault rock materials by means of field analysis of an exhumed fault and laboratory experiments, in order to determine the processes responsible of the efficiency of two thermally-activated slip-weakening mechanisms: the thermal pressurization and the moisture-drained weakening mechanism. The field study was conducted on well-exposed outcrops of a potentially active strike-slip fault that belongs to the Western Chugoku fault system (Japan): the Usukidani fault. The experimental work was conducted in the rock deformation laboratory at Kyoto University. The primary results of this research are exposed below.
The hydrological and poroelastic properties of gouge and breccia of the Usukidani fault have been determinated on laboratory from retrieved samples. The thermal pressurization process has been investigated in cases of slip along a principal slip zone and along splay faults branching off the principal displacement zone, from a numerical model constrained by these hydraulic data. Modelling results suggest that thermal pressurization is a viable process only as long as the rupture remains located in the central gouge zones or in mature splay fault gouge zones.
To identify the particle dynamic processes responsible of slip-weakening in clay-rich seismic slip zones, several rotary-shear experiments were conducted at coseismic slip-rates (equivalent to 0.09, 0.9 and 1.3 m/s) for different gouge water contents: wet initial conditions or dry initial conditions. The representative mechanical behavior of the simulated faults show a slip-weakening behavior, whatever initial moisture conditions. Detailed examination of gouge microstructures obtained at the residual friction stage in wet and dry initial conditions allows to define two types of microstructure implying two deformation regimes: a rolling regime with formation of clay-clast aggregates, and a sliding regime with formation of a complex shear zone localized at the gouge-wall-rock interface. The observed slip-weakening behavior of simulated faults appears to be related to a decrease of the proportion of grain rolling to grain sliding with increasing slip displacement and appears to be favored by the development of clay-clast aggregates, which is controlled by water content.
From a numerical model (P2 FEM) based on shear stress data, the temperature rise on the simulated fault gouge with increasing slip displacement is approached. Modelling results suggest that the slip-weakening distance dc might represent the necessary slip distance to produce and diffuse enough heat throughout the fault gouge layer to break liquid capillary bridge and to drain off completely pore water and adsorbed water at contact area of gouge particles, that is the thermally-activated moisture-related weakening mechanism.
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Contributor : Sébastien Boutareaud <>
Submitted on : Thursday, March 13, 2008 - 9:14:09 AM
Last modification on : Wednesday, December 2, 2020 - 9:56:06 AM
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Sébastien Boutareaud. SLIP-WEAKENING MECHANISMS AT HIGH SLIP-VELOCITIES: INSIGHTS FROM ANALOGUE AND NUMERICAL MODELLINGS. Tectonics. Université de Franche-Comté, 2007. English. ⟨tel-00263691⟩

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