Shear wave velocity and attenuation tomography acquired from seismic ambient noise data analysis in a complex collisional area at the edge of the East European Craton

The collisional area between the ALCAPA microplate and East European Craton across the Carpathian Orogen, is one of the most intriguing geological areas in Europe.  Here, a variety of tectonic processes are occurring simultaneously, including extensional basins, oceanic subduction, post-collisional volcanism, and active crustal deformation due to the push of the Adria plate or the pull of the actively detaching Vrancea slab, creating it a distinctive tectonic setting.

To explore the lithospheric structure of this collision region, broadband stations operating in the Carpatho-Pannonian area between 2006and 2022 were transformed into virtual sources by cross-correlating simultaneous noise recordings at pairs of stations in the frequency domain and stacking the cross-correlations to obtain one inter-station cross-correlogram per pair (Empirical Green functions). Rayleigh and Love phase velocities, as well as Rayleigh wave attenuation coefficients, were measured and mapped at six discrete periods (5, 10, 15, 25, and 30s) using the latest multiscale seismic imaging algorithms. We used a least-squares inversion approach based on ray theory with adaptive parameterization to map the lateral variations in surface-wave velocity, whereas the attenuation structures were revealed by mapping the frequency-dependent Rayleigh-wave attenuation coefficient.

Our results reveal a strong correlation between geology and tomographic images, suggesting a highly heterogeneous crust. An inverse correlation trend between Rayleigh wave phase velocity and attenuation maps was obtained for all period ranges, revealing a contrast between high attenuation features from the Pannonian Basin, including intra-Carpathian areas, and stable platform regions placed in front of the Carpathians. The shallow crust shear velocity model shows low velocities beneath Neogene and Paleozoic sedimentary basins and volcanic regions and high velocities under collisional fronts. In the middle to lower crust (25–30 km), high shear velocities beneath the Pannonian basin are in agreement with the previous findings.