Seismotectonics of a low-deformation area: the central Western Alps (Italy)

Abstract

This work is based on the integration of detailed field mapping, structural analysis and updated seismological data for the central Western Alps. In this area, three regional, steeply-dipping fault systems seem to be connected to the current seismic activity: the Longitudinal Faults, in the western part, the Transverse Faults, in the central part, and the Col del Lis-Trana Deformation Zone, in the eastern part. Structural and seismological data suggest that since the Late Oligocene, a dextral transtensive regime has been active in this area. The Canavese Line seems to represent the structure that decouples this stress regime, acting inside this sector of the chain, from the transpressive regime that characterizes the adjacent westernmost Po Plain. At a regional scale, this transtensive regime is induced by the coexistence of two driving forces: the counterclockwise rotation of the Adria plate and the body forces acting inside the chain. These two different forces, induced respectively, the dextral and normal components of movement along the major faults bounding the Western Alps. The data fit in a model of dextral transcurrence at the scale of the Western Alps. The data presented in this work contribute to an updated seismic macrozonation of the western Alpine chain, a very populated area where, up to now, only marginal seismotectonic studies have been carried out.