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Propagation des intrusions basaltiques. Modélisation analogique et suivi temporel par inversion des données de déplacements

Abstract : We study magma transport in the upper crust by propagation of a buoyancy-driven fluid-filled crack. Two schools of thought formalize the modelling of this phenomenon. They provide a framework to interpret either the geometrical aspects (shape, trajectory) when fluid viscosity is neglected, or the temporal aspect (flow velocity of the fluid) when, resistance to fracturation of the medium is neglected. We use two complementary approaches~: temporal in situ monitoring by inversion of displacement data and analogue modelling, in order to constrain both the geometry and the timing and to discriminate the field of application of each school of thought.We combine InSAR and GNSS data in an original inversion procedure, taking advantage of both the spatial coverage of InSAR and the temporal resolution of GNSS. The method is applied to study the complex propagation (changes of direction and velocity) that led to the eruption of 26 May 2016 at Piton de la Fournaise. This makes it possible to validate the method and provides new constraints on the supply and triggering of this eruption. In the laboratory, we are investigating the influence of fluid viscosity on the velocity and trajectory of a buoyancy-driven fluid-filled crack during ascent in the presence of a heterogeneous stress field. We used gelatine an analogue of elastic host-rock and we show that the addition of salt increases its resistance to fracture. We also show that the trajectory is the result of a competition between the internal pressure, the external stress field and the crack length. Finally, we highlight the influence of the properties of the medium, as well as those of the injected fluid on the propagation velocity and the velocity variations during ascent in the presence of a heterogeneous stress field.
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Delphine Smittarello. Propagation des intrusions basaltiques. Modélisation analogique et suivi temporel par inversion des données de déplacements. Sciences de la Terre. Université Grenoble Alpes, 2019. Français. ⟨NNT : 2019GREAU033⟩. ⟨tel-02491365⟩

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