# The First Seismic Imaging of the Holy Cross Fault in the Lysogory Region, Poland
## 1 Introduction  
The Holy Cross Mountains (HCM) in central Poland represent an isolated outcrop of Paleozoic rocks within the Trans-European Suture Zone, marking the transition between the Precambrian East European Craton and the Paleozoic mobile belts of Central and Western Europe. The Paleozoic massif of the HCM is composed of sedimentary rocks, ranging in age from Cambrian to Carboniferous and which were folded in variscan orogen and then covered by Permian to Mesozoic sediments [1]. They were exhumed during the Late Cretaceous to Paleocene periods, later overlaid by Miocene marine deposits, and re-exhumed in the Neogene period. Based on the differences in sedimentary succession and tectonic evolution, the HCM had been divided into two regions, the northern (the Lysogory Region--NHCM) and the southern (the Kielce Region--SHCM). In general, the NHCM is characterized by a greater continuity of sedimentation and a more deep-water nature of deposition. In contrast, SHCM is characterized by a greater number of sedimentary gaps and more shallow-water sediments [2].  
These two regions (NHCM and SHCM) are separated by the main Holy Cross Mountain Fault (HCF). The HCF is commonly interpreted as a suture zone separating fragmentsof crust of different paleogeographic history. However, paleogeographic interpretation of this fault changed in time from the border between Malopolska terrane and the East European Craton to the border between Lysogory and Malopolska terranes [3]. The latest large-scale refraction experiment [4] and based on that 3D crustal structure model of Poland [5] shows that the structure of the whole area, including the Malopolska block, is identical and should be interpreted as a part of the East European Craton [6]. In turn, the kinematics of the HCF itself is interpreted variously: as a thrust or reverse fault [7,8] and as a regional scale strike-slip fault [9,10].  
The importance of understanding the tectonic origins of the HCF has long been understood and hence it has been the subject of intensive research. Most of these have focused on documenting the facies differences between the NHCM and SHCM and to a lesser extent have relied on tectonic structural methods. Despite the wealth of geological knowledge, geophysical methods have been scarcely used to image the internal structure of the HCM. Geophysical imaging of near-surface faults is challenging due to complex structures existing in a very shallow subsurface, including weathering, strong anisotropy, and groundwater saturation [11]. Such variations result in strong seismic velocity variations that make clear seismic imaging difficult [12]. Small-scale heterogeneities that typically exist in fault zones require specific high-resolution surveys to allow seismic velocity analysis [13]. In this paper, we present a small-scale 2D seismic profile located precisely at the main Holy Cross Fault, along with images of the structure of the Krzemianka block, which belongs to the Lysogory Unit. Additionally, we aim to demonstrate that advanced but still low-cost, academically funded seismic profiles [14] can substantially enhance the geological interpretation of fault networks in areas where no seismic surveying was performed previously.