Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

466 PATA Days 2024 Paleostress reconstruction Cave passages can act as indicators of fault displacements once the karst morphology has been offset. In cases where cave passage offsets do not show slickenlines, the line orientation between two points connected the pre-faulting features is used as a fault slip vector, with its length indicating the offset (Szczygieł et al., 2022). To determine the orientation of the principal paleostress axes (σ1, σ2, σ3), the PBT method was employed using the TectonicsFP software (Ortner et al., 2002). A set of eight reverse (Fig. 2A) and one dextral fault has been recorded within the TFD in three caves. The inversion revealed that faults were reactivated under NE-SW horizontal shortening. Slightly different results were obtained from the Tennengebirge massif, where the dextral Lammertal fault affected cave passages (Fig. 2B) with NNW-SSE shortening andWSWextension. The paleostress tensors were reconstructed from the dataset of 12 strike-slip and reverse faults measured in tree caves. Geochronology Within the TFD, the reverse fault in Interessante Höhle (Hagengebirge) broke the flowstone dated to 539 ka (+110/-72), and on the other side of the Bluntau valley in Dependance cave (Göll) the reverse fault was reactivated between 129.2±2.3 and 92.0±1.2 ka, as indicated by broken and overgrown flowstone. In the Tennegebirge, no speleothems deformed directly by faults were found. Yet in Bierloch cave, where dextral faults parallel to the Lammertal fault have been recorded, a huge piece of flowstone with stalagmites was detached from the ceiling. The collapse is located only a meter from the fault plane, which may indicate that the offset triggered it. The fallen speleothem contains two deformations dated to 288±9 and 124±7 ka. S U M M A R Y Structural and geochronological data reveal Late Pleistocene NNE-SSW shortening of the Northern Calcareous Alps. This led to the reactivation of reverse faults within the TFD, serving as a restraining band within the complex sinistral KLT system. The dextral motion along the Lammertal fault counterbalances the westward movement of the southern KLT block. Reactivation of dextral displacement within the fault zone, likely affecting caves on the northern flank of the Tennengebirge, occurred around 288 ka and later around 123 ka, coinciding with the reactivation of reverse faults in the TFD within the Göll massif. Thus, we provide framed-in-time geological evidence Fig. 2: Field examples of studied faults A) reverse offset in Dependance Cave, Göll; B) dextral fault in Birloch Cave, Tennengebirge