Present-day vertical isostatic readjustment of the Western Alps revealed by numerical modelling and geodetic and seismotectonic data

Abstract The active tectonics of the Western Alps reveals contrasting regimes: ongoing extension at the heart of the chain and transpression–compression at its external sectors. The active processes currently affecting this region are still a matter of debate. The classical models proposed in the literature invoke: Eurasia–Adria plate collision, counterclockwise motion of the Adria microplate, slab retreat of the subducted continental lithosphere and slab-detachment. More recently, several authors prefer the hypothesis of tectonics driven by isostasy–buoyancy forces. To better understand the influence of these processes on the velocity, strain and stress fields at the surface and in the crust, we developed 2D viscoelastic numerical models along a vertical cross-section perpendicular to the Western Alps. We run our models with different driving forces in order to investigate, one by one, the geodynamic processes proposed in the literature. Results are compared with available geodetic, geological and seismotectonic data. In order to bring into coincidence model predictions and observations, an important vertical isostatic readjustment must be included in the modelling, together with a slight horizontal compression (0.5 mm year −1 ), probably due to Africa–Eurasia convergence. We show that the subduction process in this Alpine region is likely to be dead and that buoyancy forces may be dominating the present-day tectonics.