Italian and Alpine three-dimensional crustal structure imaged by ambient-noise surface-wave dispersion

Abstract

We derive the 3-D crustal structure (S wave velocity) underneath Italy and the Alpine region, expanding and exploiting the database of ambient noise Rayleigh-wave phase- and group-velocity of Ver- beke et al. (2012). We first complement the database of Verbeke et al. (2012) with a dense set of new ambient-noise-based phase-velocity observations. We next conduct a suite of linear least squares inversion of both phase- and group-velocity data, resulting in 2-D maps of Rayleigh-wave phase and group velocity at periods between 5 and 37 s. At relatively short periods, these maps clearly reflect the surface geology of the region, e.g., low velocity zones at the Po Plain; at longer periods, deeper structures such as Moho topogra- phy under Alps and Apennines, and lower-crust anomalies are revealed. Our phase- and group-velocity models are next inverted via the Neighbourhood Algorithm to determine a set of one-dimensional shear- velocity models (one per phase/group-velocity pixel), resulting in a new three-dimensional model of shear velocity (vS) parameterized in the same way as the European reference crustal model EPcrust. We also show S how well vS is constrained by phase and group dispersion curves. The model shows the low velocity area beneath the Po Plain and the Molasse basin; the contrast between the low-velocity crust of the Adriatic domain and the high-velocity crust of the Tyrrhenian domain is clearly seen, as well as an almost uniform crystalline crust beneath the Alpine belt. Our results are discussed from the geological/geodynamical stand- point, and compared to those of other, interdisciplinary studies.