From seismic re-processing to mechanic modelling, a new interpretation of the TRANSALP seismic section as a base for future geothermal energy projects, lower Inn Valley, Tyrol, Austria

In western Austria, especially in Tyrol, the potential for geothermal energy use is unexplored. The project GeoEN Inntal is aiming to determine this potential and the risks for the use of geothermal energy in a complex tectonic setting in the Inn valley. The valley is bordered by the Permo-Mesozoic sedimentary succession of the Northern Calcareous Alps in the north and the south-east, as well as Upper Austroalpine basement units in the south. Since the early Late Cretaceous, during Eoalpine orogeny, the Austroalpine basement and its Mesozoic cover were involved in nappe stacking and folding. The nappe stack was again refolded and faulted in the Palaeocene-Eocene collision of Adria and the European distal margin, as well as in Oligocene-Miocene, when post-collisional processes lead to an eastward extrusion of crustal blocks, out-of-sequence thrusting and the development of major faults. One of these faults is the Inntal shear zone, a sinistral ENE-trending shear zone, controlling the course of the Inn valley (“Inntal” in German). The shear zone has a multi-phase activity and is kinematically linked with the Brenner normal fault south of Innsbruck, the Alpine basal thrust at the Alpine front, and the Sub-Tauern ramp, rooting below the Tauern window. As the deep subsurface of the Inn valley was only explored geophysically, but no exploration boreholes were drilled, little is known about these structures at depth. Here we present the reprocessed Inntal part of the TRANSALP seismic section, which serves as a base for multidisciplinary modelling approaches. As part of the GeoEN Inntal project, we present first results from our 3D modelling of fault geometry, results from mechanical modelling of the Inntal shear zone, as well as first temperature gradient assessment from hydrological modelling.