# The First Seismic Imaging of the Holy Cross Fault in the Lysogory Region, Poland
## 2 Geological Framework  
The tectonic evolution of the HCM reflects complex interactions from the Cadomian to Variscan orogenies, influenced by its proximity to the Baltic margin. The Variscan orogeny induced significant N-S-directed shortening after Visean times, resulting in large-scale folding within the Kielce and Lysogory zones [15]. A subsequent tectonic phase during the Maastrichtian-Paleocene uplift caused brittle deformation, modifying earlier folds. Faulting within the HCM includes both longitudinal and transverse faults, characterized by a combination of strike-slip and either normal or reverse-slip components in both regions [16]. The HCM's structure is a Paleozoic core exposing highly deformed pre-Permian rocks over an area of about 90 by 40 km (as shown in Figure 1). This core is bordered by a Mesozoic margin of less-deformed Permian-Mesozoic rocks to the north, west, and southwest. The core was exhumed during the Late Cretaceous-Paleocene inversion of the German-Polish Basin, and in the Miocene, both the core and margin were covered by Carpathian foreland basin sediments, enclosing the core to the south [17]. The HCM fold belt was generated post-Visean through buckle folding of sedimentary rock strata. Fold growth ceased before the onset of the Late Permian and during this folding phase, extensive folds developed at a regional scale. Faults with a significant strike-slip component likely formed in a subsequent faulting phase or during the post-folding deformation stage [18]. Accurate determination of the timing of these strike-slip events and the distribution of strain across individual faults is complex, given that the HCM fold belt underwent at least two primary phases of strike-slip faulting: (I) during the Late Paleozoic and (II) in the Maastrichtian to Paleocene interval [19,20]. Similarities in the shortening directions--NNE-SSW during the Late Carboniferous and generally NE-SW during Maastrichtian/Paleocene folding events--further complicate the interpretation of fault timing. This suggests the development of new faults and reactivation of some pre-existing faults in a strike-slip mode during both the later folding phase and the younger strike-slip phase (II) [21]. The Lysogory region consists of two main tectonic units at the map scale: the Lysogory Thrust Sheet in the south and the Bronkowice Anticline in the north, separated by the Bodzentyn Syncline [22]. The Lysogory region contains an approximately 7 km thick (as shown in Figure 2), largely continuous succession of Mid-Cambrian to Late Devonian sedimentary layers, beginning with the Middle Cambrian Gory Pieprzowe Formation and culminating in Late Devonian Farnenian strata, with a local hiatus in the Pragian period. The Late Silurian-Early Devonian stratigraphy is not well defined, leading to varied classification schemes. For consistency, the succession is divided into the Wydryszow/Rzepin and Klonow/Bostow series [23]. The Wydryszow Series is a Mid-Late Ludlowian flysch deposit in a foreland basin setting, while the Rzepin Series, with shallow marine characteristics, is composed of varied clastics from the Late Ludlowian-Pridolian. The overlying Klonow/Bostow Series, spanning the Late Pridolian-Lochkovian, includes marine and continental layers. A brief hiatus in the Early to Middle Pragian period is followed by the Barcza and Zagorze formations, which are transgressive and estuarine in nature, measuring 650-900 m thick combined [8; 24]. In contrast, the Kielce region has a thinner, less complete Upper Silurian-Lower Devonian section, often missing entirely, with the Emsian deposits (correlative  
Figure 1: **(A)** Tectonic map of Poland with marked Holy Cross Mountain region (HCM). **(B)** Geological map of the Holy Cross Mountains (after [22], modified). **(C)** Geological map of the study area. Red line shows the seismic profile crossing Holy Cross Fault (HCF). with the Barcza Formation in the Lysogory Region) frequently lying atop Lower Cambrian layers.