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Avis d soutenance de Thèse _ Séverine Furst

Séverine Furst

Soutiendra sa thèse

Optimisation multi-objectifs pour l'inversion jointe de données géodésiques

Le 1er octobre 2018 à 13h00 salle 23.01

Devant le jury composé de :

M. Bijan Mohammadi (IMAG, UM)...................................................Directeur de Thèse

M. Luis Riviera (EOST, U. Strasbourg)..............................................Rapporteur

M. Riad Hassani (Géosciences Azur, U. Sophia Antipolis).............Rapporteur

M. Jean Chéry (Géosciences Montpellier, UM)................................Co-Directeur de Thèse

Mme Christelle Tiberi (Géosciences Montpellier, UM)...................Examiniateur

M. Dominique Dubucq (Total, S.A.)

M. Michel Peyret (Géosciences Montpellier)

 

The Earth’s surface is shaped by global processes such as subduction and rifting zones, but it can also be affected by numerous local processes like volcanic events, landslides or earthquakes. Along with these natural processes, anthropogenic activities including extraction and storage of resources (e.g.salt, ore, hydrocarbons), shape the Earth at different space and time scales. These mechanisms produce deformation of the ground ranging from tens of nanometers in the case of a fracture stimulation up to several meters for landslides and earthquakes. These permanent changes of the Earth’s surface are measured using instruments and techniques developed in geodesy. Geodetic techniques provide a time-space record of the surface deformation above various kinds of reservoirs among which volcanoes are probably the most monitored and studied because of their high associated hazards and/or risk. Salt mines also host some geodetic instruments or surveys, due to legal obligations asking for the monitoring of the induced deformation at the surface. Hydrocarbons reservoirs are subjected to strict regulations mainly to prevent from polluting surrounding fauna and flora and long-term monitoring is requested. These three geological reservoirs (magmatic, salt and hydrocarbons) need to be monitored over long time period for hazard assessment. Because they all display common features, we approach this issue developing a common methodology. Due to incoming, deforming, moving, extracting or erupting materials, these deep reservoirs are subjected to volume variations inducing modifications in the surrounding medium up to the surface. In this work, we are interested in the quantification of these volume variations, assuming the origin of the deformation. We consider the ground displacements that can be observed in volcanic systems, salt mining and unconventional reservoirs and the following geodetic instruments and techniques: GPS, tiltmeters, levelling surveys and InSAR interferograms. Linking these observations to an assumed physical process is permitted using an inverse strategy. By doing so, we aim at retrieving the parameters defining the process that produces modelled data explaining at best the observed ones. Therefore, we propose in this manuscript a common methodology of inversion based on a global optimization algorithm (Mohammadi and Saïac, 2003). This allows us to reach at low computational cost the optimal solution of problems of different complexities.

Keywords : Geodesy, Inversion, Geological reservoirs, Optimization, Modelling