Abstract
The Western Alps is one of the most seismically active areas in France. The question of the origin of this seismicity is debated: indeed, the seismic and geodesic extension observed in the Alps is not compatible with a classical tectonic convergence hypothesis. The hypothesis of surface processes as a source of seismicity and deformation is advanced and studied in this thesis. First, the geodesic strain rates are re-evaluated by filtering the measurement noise using Gaussian smoothing, using three different datasets. The synthetic strain rate field thus calculated shows amplitudes of the order of 1-2 x 10-9 yr-1, with extension rates oriented N-S in the Swiss Alps, and NW-SE in the French Alps, surrounded by rates of radial shortening in the foreland and strike-slip in the Southern Alps. These deformation rates are used as tools for comparison with modeling of postglacial erosion and rebound processes. Through a thin plate analytical modeling approach, current strain rates and stresses are calculated for these two processes. This study shows that the geodetic signal is largely influenced by the postglacial rebound, which can represent at least half of the vertical signal of the uplift of the Alps, erosion representing the other half. The deformation styles of the sum of the two processes are consistent with the geodetic field, but only reaching 30 to 50% of the geodetic amplitude. However, despite the importance of the postglacial rebound in the current signal, this study shows that this process tends to inhibit seismicity. The stresses generated by erosion, on the other hand, can be at the origin of seismicity in the Western Alps. This observation suggests that in the Western Alps, the geodetic fields are not representative of seismicity, and that they are therefore not a good proxy for seismic hazard models in this area.