Shear heating in granular layers
Identifieur interne : 00C139 ( Main/Exploration ); précédent : 00C138; suivant : 00C140Shear heating in granular layers
Auteurs : Karen Mair [États-Unis] ; Chris Marone [États-Unis]Source :
- Pure and Applied Geophysics [ 0033-4553 ] ; 2000.
Descripteurs français
- Pascal (Inist)
English descriptors
- KwdEn :
Abstract
Heat-flow measurements imply that the San Andreas Fault operates at lower shear stresses than generally predicted from laboratory friction data. This suggests that a dramatic weakening effect or reduced heat production occur during dynamic slip. Numerical studies intimate that grain rolling or localization may cause weakening or reduced heating, however laboratory evidence for these effects are sparse. We directly measure frictional resistance (μ), shear heating and microstructural evolution with accumulated strain in layers of quartz powder sheared at a range of effective stresses (σn = 5-70 MPa) and sliding velocities (V = 0.01-10 mm/s). Tests conducted at σn ≥ 25 MPa show strong evidence for shear localization due to intense grain fracture. In contrast, tests conducted at low effective stress (σn = 5 MPa) show no preferential fabric development and minimal grain fracture hence we conclude that non-destructive processes such as grain rolling/sliding, distributed throughout the layer, dominate deformation. Temperature measured close to the fault increases systematically with σn and V, consistent with a one-dimensional heat-flow solution for frictional heating in a finite width layer. Mechanical results indicate stable sliding (μ ∼0.6) for all tests, irrespective of deformation regime and show no evidence for reduced frictional resistance at rapid slip or high effective stresses. Our measurements verify that the heat production equation (q = μσnV) holds regardless of localization state Or fracture regime. Thus, for quasistatic velocities (V ≤ 10 mm/s) and effective stresses relevant to earthquake rupture, neither grain rolling/sliding or shear localization appear to be a viable mechanism for the dramatic weakening or reduced heating required to explain the heat flow paradox.
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Le document en format XML
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<profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Q</term>
<term>SEM data</term>
<term>San Andreas Fault</term>
<term>deformation</term>
<term>fabric</term>
<term>fault gouge</term>
<term>fracturing</term>
<term>friction</term>
<term>heat flow</term>
<term>heat production</term>
<term>microstructures</term>
<term>quartz</term>
<term>rupture</term>
<term>scanning electron microscopy</term>
<term>shear</term>
<term>shear stress</term>
<term>slip</term>
<term>temperature</term>
<term>velocity</term>
</keywords>
<keywords scheme="Pascal" xml:lang="fr"><term>Faille San Andreas</term>
<term>Argile faille</term>
<term>Flux géothermique</term>
<term>Cisaillement</term>
<term>Frottement</term>
<term>Production chaleur</term>
<term>Déformation</term>
<term>Vitesse</term>
<term>Quartz</term>
<term>Fabrique</term>
<term>Température</term>
<term>Facteur Q</term>
<term>Rupture</term>
<term>Contrainte cisaillement</term>
<term>Microstructure</term>
<term>Glissement</term>
<term>Fracturation</term>
<term>Microscopie électronique balayage</term>
<term>Donnée MEB</term>
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<front><div type="abstract" xml:lang="en">Heat-flow measurements imply that the San Andreas Fault operates at lower shear stresses than generally predicted from laboratory friction data. This suggests that a dramatic weakening effect or reduced heat production occur during dynamic slip. Numerical studies intimate that grain rolling or localization may cause weakening or reduced heating, however laboratory evidence for these effects are sparse. We directly measure frictional resistance (μ), shear heating and microstructural evolution with accumulated strain in layers of quartz powder sheared at a range of effective stresses (σ<sub>n</sub>
= 5-70 MPa) and sliding velocities (V = 0.01-10 mm/s). Tests conducted at σ<sub>n</sub>
≥ 25 MPa show strong evidence for shear localization due to intense grain fracture. In contrast, tests conducted at low effective stress (σ<sub>n</sub>
= 5 MPa) show no preferential fabric development and minimal grain fracture hence we conclude that non-destructive processes such as grain rolling/sliding, distributed throughout the layer, dominate deformation. Temperature measured close to the fault increases systematically with σ<sub>n</sub>
and V, consistent with a one-dimensional heat-flow solution for frictional heating in a finite width layer. Mechanical results indicate stable sliding (μ ∼0.6) for all tests, irrespective of deformation regime and show no evidence for reduced frictional resistance at rapid slip or high effective stresses. Our measurements verify that the heat production equation (q = μσ<sub>n</sub>
V) holds regardless of localization state Or fracture regime. Thus, for quasistatic velocities (V ≤ 10 mm/s) and effective stresses relevant to earthquake rupture, neither grain rolling/sliding or shear localization appear to be a viable mechanism for the dramatic weakening or reduced heating required to explain the heat flow paradox.</div>
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