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Pertinence du formalisme des transitions de phase pour aborder la mécanique des objets géologiques

Abstract : In th is work, we analyze in detail the concept of phase transitions and discuss how it can be useful to understand the non linear and scale invariant dynamics of the Earth crus!. ln particular, we attempt to clarify the necessary conditions and the implications of the critical state of a system, and discuss whether the geomechanical properties of the Earth crus! fit these conditions. We review recent approaches which have been proposed to interpret the rupture of materials, the large scale deformation of the Earth crust, or the friction along a fault, in the framework of phase transitions. We shed Iight not only on the concept of criticality, but also on other mechanisms of phase transitions which produce scale invariance. We then apply concretely this formalism on three different problems: the mechanics of eruptions in a volcano, the deformation of an hydrocarbon reservoir, and the viscoplastic deformation of an ice sample. The variety of these applications illustra tes that the formalism of phase transitions is a general and powerfui tool to analyze geomechanical problems. First, we propose a model for reservoirs of basaltic volcanoes composed of many magma lenses in interaction, where eruptions result from a cascade redistribution of magma from lens to lens up to the surface. This model is in agreement with the statistics of eruptions recorded on the Piton de la Fournaise (Reunion island). We then focus on a hydrocarbon field (Lacq, France), where we observe that very low-frequency variations of the loading rate induced by gas extraction has an impact on the fracturing pattern of the reservoir. We discuss the implications of this finding for indus trial purposes as weil as for the mechanics of the Earth crust. Lastly, we show that dislocation-driven viscoplastic deformation of materials, Iike brittle deformation, exhibit scale invariance and can be understood in the framework of phase transitions.
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Submitted on : Thursday, October 25, 2012 - 5:00:39 PM
Last modification on : Thursday, November 19, 2020 - 3:54:28 PM
Long-term archiving on: : Saturday, December 17, 2016 - 5:26:26 AM

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  • HAL Id : tel-00745548, version 1

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Franz Lahaie. Pertinence du formalisme des transitions de phase pour aborder la mécanique des objets géologiques. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2000. Français. ⟨tel-00745548⟩

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