2-D S-velocity and radial anisotropy across the southern Vienna Basin from nodal probabilistic ambient noise tomography

During summer 2025, we deployed 140 5-Hz geophones along a profile running from the foothills of the eastern Alps to the Danube basin. Using ambient noise interferometry, we extract Rayleigh- and Love-wave dispersion curves at short periods (0.8–5 s) and develop a high-resolution radially anisotropic shear wave velocity model of the southern Vienna basin. The isotropic shear-wave velocity model reveals the Neogene sediments and the sedimentary units of Northern Calcareous Alps (NCA). We also map a normal fault controlling the shape of the western edge of the basin. Moreover, we find that the anisotropic structure of the southern Vienna basin is characterized by two distinct layers. The upper 1–1.5 km exhibits weakly negative to weakly positive radial anisotropy, whereas deeper levels are marked by strong positive anisotropy. We interpret the shallow negative anisotropy as reflecting the presence of vertically oriented fractures. Beneath the Neogene Basin, the NCA nappe stack displays strong positive anisotropy, consistent with its thin-skinned, low-angle thrust architecture. In contrast, where the NCA crops out to the northwest, the anisotropic signature is weaker and locally reversed.