First Results of 3D Travel Time Tomography of the Ligurian Sea and Coastal Western Alps

The Ligurian Sea is a highly complex tectonic setting lying between two major orogeny, theWestern Alpine belt and the Apennine system. The sea formed as a back-arc basin related to the Apennines-Calabria subduction zone retreat. Opening began in the late Oligocene and continued into the early Miocene by the counter-clockwise rotation of the Corsica-Sardinia block. The area is now under compression with shortening of 0.3-1.5 mm/year along the northern margin. The regions tectonic activity has produced large topographic gradients, with heights of >3 km in the Alps descending to depths of 2.5 km in the center of the Ligurian Basin over a horizontal distance of only 100 km. The crust and upper mantle show strong heterogeneity, and a strong gradient in the Moho which is fairly shallow in the basin center, 12.5 km depth, and then deepens sharply at the coastlines to 50 km under the Alps and 25 km under Corsica.The area has hosted large, destructive earthquakes, such as the 1897 Mw 6.3-7.5 Imperia earthquake, such earthquakes could have a devastating effect on the densely populated Ligurian sea coast. To better estimate these risks, we must improve our understanding of shallow and deep structures and processes, from faulting in the basin to the change in subduction polarity between the Alpine and Adriatic slabs. In this way we can better estimate the seismic hazard posed to cities along the coast, as well as broadening our understanding of the evolution of the Alpine orogen. In the frame of the DFG Priority Program Mountain Building Processes in Four Dimensions (MB-4D), we will link the deep structure to surface deformation using body wave tomography covering the Ligurian Sea from Corsica to the South-Western Alps. In this poster we present the first results of 3D body wave tomography of the Ligurian Basin and surrounding region. We picked the first arrivals from two active seismic profiles at land stations and Ocean Bottom Seismometers (OBS) and used these as input for the inversion program TOMO3D. The code also allows for passive sources and anisotropy, both of which will be explored in the future. Land stations and OBSs used were installed in the frame of the European AlpArray initiative or are permanent stations from the Mediterranean seismological networks.