Seismic potential analysis of a lithospheric sector north-west of the Alps

The north-west of the Alps is an intraplate domain with very slow deformations. So, it seems difficult to determine the probability of occurrence of a lithospheric earthquake (magnitude greater than 7) from microseismic observations. Such observations are superficial processes with little relation to deeper and bigger ones. The aim is to determine the seismic potential of a lithospheric sector north-west of the Alps, studying the stress field generated by a gravity driven model. This model is 360 km by 400 km by 230 km deep, centered on the west alpine fossil subduction and going up to the north of Strasbourg. The study of the north-west alpine structures shows the importance of the alpine orogen which generates variations in depth of the lithospheric interfaces. A study of the stress field in the basement shows a variation of principal stress directions along the strike of the Alpine chain. Even if the absolute magnitude of stresses could not be determined a relative magnitude ratio is calculated. Results underline the importance of rheology for a gravity driven model. If an elastic rheology is modeled, calculated stress directions do not match observations. However, using an elasto-plastic rheology with a realistic geometry of the lithospheric interfaces, we can obtain stress directions coherent with the data.