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

460 PATA Days 2024 we performed 3D trenching to trace possible horizontally offset sedimentary features (Fig. 3). The trenches confirmed the youngest Holocene movements where an open fissure was infill was dated to 783-1059 AD by radiocarbon dating methods, which presents a historical event in the region. In addition, two small channels were traced across the secondary fault within the fault zone and 1 to 1.5 m offset of 3-4 ka channel was found (Fig. 4). This would be in an agreement with very first trench where the Holocene layer h1 (2.33 5.28 cal. kyr BP) has been displaced twice and h2 (0.93-2.31 cal. kyr BP) was deformed only during the latest event (Štěpančíková et al. 2019). Thus, it might be even possible that those two channels correspond to h1 and were horizontally offset twice, which would imply 0.5-0.75m per event during Mw6.3+ earthquakes. The 3D trenching combined with 3D geophysical survey revealed also the MLF zone at Kopanina site as a complex structure featured under right-lateral transpression during its youngest evolution. To see how the structure of the MLF within the Cheb basin looks like elsewhere and to confirm the surface-breaking Holocene earthquakes, which were quite surprising in the intraplate region, we trenched the second site close to waterdam Horka, in the Libocký Brook valley floor (Fig. 2). At Horka site two trenches were excavated, first one crossing the anticipated trace of the fault predicted by geophysics and by projected fault line from the adjacent morphologically more pronounced segments. The Fig. 3: Orthophoto of the 3D trenching on the Kopanina site. Red dashed line – the faults documented in the trenches. Fig. 4: Late Holocene channel horizontally offset by 1-1.5m revealed by micro-trenching.