3-D Surface-Wave Tomography of the European Alpine Lithosphere from Ambient-Noise and Earthquake Two-Station Measurements

Our new high-resolution tomography images shed light on fundamental issues concerning the tectonic processes that led to the formation of the European Alps. We study, in particular, the mechanism of subduction at the triple junction between the Adriatic, European and Pannonian domains. Different theories exist concerning the geometry of the switch in subduction polarity of the Adriatic plate, from being the upper plate in the Europe-Adria collision to being subducted underneath the Carpathians. This involves also a potential slab break-off of the European plate and a following reversal from lower to upper plate. We compile a data set of Love- and Rayleigh-wave phase-velocity measurements using more than 25,000 station pairs, and including both ambient-noise and earthquake-based two-station correlations. This allows us to constrain seismic structure from the shallow crust down to 200 km depth. We determine phase velocities from ambient noise in the frequency domain using an automated algorithm. In better-sampled regions we achieve a lateral resolution of 20 km close to the surface. We derive high-resolution maps of sedimentary basins and of the crustal structure and thickness under the Alps, constraining the complex interaction of the microplates involved in the Alpine collision. In some places we are able to trace the signature of subducting plates from the bottom of the crust to 200 km depth. We propose that our 3-D model could serve as a new reference for the Alpine crust, and that our method be applied to new seismic records from the AlpArray deployment.