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

472 PATA Days 2024 Kinematics and geodynamic mechanism Despite local variations, NE-SW compression with NW-SE extension prevails when considering both the Podhale and Orava basins and the Tatra Mts. This trend is apparent in both present instrumental data (Jarosinski, 2006; Wiejacz & Debski, 2009; Bednarik et al., 2016) and the limited geological record (Szczygieł, 2015; Szczygieł et al., 2024). Although Peskova et al. (2009) and Vojtko et al. (2010) inferred W-E Quaternary extension, with linked N-S compressional stress, this was not based on the faulting of Pliocene sediments, hence may be subject to substantial error. This suggests the supra-regional prevalence of NNW maximum horizontal stress directionssince the Pleistocene. However, so far, no geological evidence has supported the Pleistocene continuity of the SSW- NNE regional shortening. The Brzegi fault, however, serves as such evidence. Its NNW-SSE strike-slip movement with dextral motion aligns with this supra- regional stress regime. Therefore, it provides evidence of the post-Miocene continuation of the far- field effect of eastward Alpine extrusion on the Carpathians, which according to Peresson and Decker (1997) terminated in the Pliocene. Significantly slower than during the Miocene, but still Pleistocene extrusion of the Alps was recently proven (Plan et al., 2010; Szczygieł et al., 2022). The far-field effect includes the sinistral movements along the Carpathian Shear Corridor, including the sinistral Prosečné-Krowiarki and Ružbachy faults (Marko et al., 2017). In this context, the dextral Brzegi fault, as part of the broader Białka fault zone, would correspond to the R' shear within the supra-regional sinistral transtension and compensate CCW rotation of blocks inside the sinistral Carpathian Shear Corridor. A significant change from the Miocene dynamics would be a change in regime from transpression (Peresson and Decker 1997; Sperner et al., 2002; Ludwiniak et al., 2019) to transtension, as indicated by the dominance of NE-SW extension in the paleostress reconstruction (Vojtko et al., 2010; Szczygieł, 2015; Szczygieł et al., 2024) and the opposite vertical movement of the reactivated Brzegi fault compared to the original offset. C O N C L U S I O N The collected data are not definitive in the identification of the origin of the morphological scarp. Nonetheless, a comprehensive analysis of all gathered data allows for the hypothesis that assuming a seismic- tectonic origin of the scarp in Brzegi, the associated fault may have generated earthquakes of magnitude ~M6, although the preserved scarp is much too short for such an earthquake, which so far remains a mystery. Furthermore, the documented dextral offset fits into the context of the late Neogene tectonic evolution of the Western Carpathians. Conversely, the degree of scarp erosion and its superposition relative to terrain features suggest that the fault in Brzegi was likely active during the late Pleistocene. A C K N O W L E D G E M E N T S The Institute of Earth Sciences at the University of Silesia financed the research. Many thanks to EwaMilan and Stefania Orawiec for allowing us to trench on their land and for their help with this project. MPWiK S.A. (Wroclaw) is thanked for providing access to the GPR unit used during the field works.