3D mechanical structure of the lithosphere below the Alps and the role of gravitational body forces in theregional present-day stress field

The present study aims to investigate how the tectonic compression due to Africa-Eurasia convergence is transmitted up to Central Europe via a thermo-mechanical model, in which a high-resolution rheological analysis is performed in the surroundings of the Alpine domain and the predicted heterogeneous lithosphere strength is accounted for to reproduce the surface strain pattern. Our rheological analysis reveals a strongly heterogeneous lithosphere strength that is characterised by steep strength gradients across the Periadriatic Lineament and the occurrence of non-competent crustal layers located below the Northern Alps, where the upper crust controls the total lithosphere strength.When the predicted lithosphere strength is included within a spherical thin sheet model to investigate the propagation of the tectonic compression due to Africa-Eurasia convergence toward Central Europe, our analysis supports the hypothesis that the N-S compressive stress dominates the gravitational body forces in the Southern Alps up to the Periadriatic Lineament. This lineament defines an abrupt transition from the strong mantle belonging to the Adriatic lithosphere to the softer mantle below the Eastern Alps, which is mechanically decoupled from the relatively stronger upper crust, thus preventing stress transmission toward the surface. Thus, in the Eastern Alps, the transmitted S-N compression would remain lower than the E-W extensional stress induced at crustal levels by the body gravitational forces associated with thick crustal layers.