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

Geothermal energy is becoming an attractive green energy since it is baseload-capable, and highly suitable for the supply of district heating in Europe. Identifying optimal locations for deep geothermal wells is essential, but such exploration typically depends on conventional active seismic surveys, which are logistically complex and costly. Recent development of nodal technology has pushed the method to higher frequencies, enabling high-resolution imaging of local and shallow velocity structure for more applied applications. In eastern Austria, the Vienna Basin is the primary target for deep geothermal production serving the city of Vienna. Meanwhile, the southern Vienna Basin also shows potential for geothermal production for smaller cities like Wiener Neustadt in lower Austria. During summer 2025, we deployed 139 5-Hz geophones along a profile running from the foothills of the eastern Alps to the Vienna 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 and Pre-Neogene sedimentary layers as well as the top of the crystalline basement. We also map a normal listric fault controlling the shape of the western edge of the basin. Moreover, we find that the anisotropic structure of the southern Vienna basin is bi-layered, with a slightly negative anisotropy in the upper 1-1.5 km depth and a strong and positive anisotropy at greater depths. We interpret the shallow negative anisotropy to reflect the influence of vertically oriented cracks, while the deeper positive anisotropy corresponds to the horizontal layering of sedimentary rocks. Combined, these findings hold significant implications for early-stage geothermal exploration in the southern Vienna Basin.