Abstract
Since its origin, the surface of the Earth has been shaped by many processes. Whether they are geological or, more recently, anthropogenic, these processes shape the topography at different scales of volume and time. Given the increase in risks (a combination of human and economic issues with subsidence or landslide hazards), the necessity to develop reliable and accurate methods of measuring these processes is clear. This is the goal of the so-called geodesic measurements.The aim of this thesis is to create a new methodology for the combination of surface displacements measured by different geodetic techniques (GNSS, InSAR, Leveling) to improve the knowledge of the deformation on many cases of studies. The first step of the combination is the harmonization of the spatial references of the deformation. Then, the velocity fields resulting from the different techniques are weighted according to their native uncertainties. Finally, a combination of these velocity fields is performed by the weighted regression kriging method. The result is a deformation grid, which, according to the data used, will present a spatial resolution in one to three dimensions. Associated to the grid, a second one of reliability index is created, taking into account the native uncertainties of each method in one hand, and the uncertainties related to the interpolation method on the other hand. The joint use of these two grids improve the discussion on the deformation.Our methodology was confronted with a case study: the subsidence of the Vauvert saline (Gard, France). This site appears ideal because of (1) its geographical situation close to Montpellier facilitating its instrumentation and measurements, (2) a subsidence is already measured, whose origin is the salt extraction between 2000 and 3000 m in depth, and (3) datasets are available in InSAR, GPS and Leveling. Two measurement periods are selected (2002-2009 and 2015-2017) because they allow the joint use of several measurement techniques. The results of the combination of velocity fields show the presence of a subsidence bowl with a maximum magnitude of 2.2 cm / year in the first period and 2.4 cm / year in the second period. Its extension reaches the southeastern area of the neighboring town of Vauvert. On the whole this subsidence (size of the bowl and magnitude) varies a little, nevertheless a zone closed to the historical sites of the Galine (east of the zone of study) presents an acceleration of the subsidence of approximately 8 mm / year between the two periods. This acceleration seems to reflect the surface effect of the closest wells purging , initiated in 2015.Finally, the use of an inversion algorithm of the data from the combination methodology (velocities and uncertainties) bring some new informations on the deformation anisotropy. An accommodation of geological structures in depth (folds, faults, detachments) is shown.