# The First Seismic Imaging of the Holy Cross Fault in the Lysogory Region, Poland
## 5 Results and Discussion  
To the best knowledge of all co-authors, this study is the first seismic imaging of the Holy Cross Fault. It demonstrates that a simple, cost-effective seismic experiment can effectively reveal geological structures in near-surface regions down to depths of approximately 400 m. Despite the compact, affordable design, the experiment provided substantial clarity in imaging and interpreting geological formations within the upper subsurface. The stream-lined implementation also makes this approach viable for environmentally sensitive or protected areas due to its minimal environmental footprint, a marked contrast to large-scale industrial seismic experiments, which tend to be both costly and intrusive [40]. Seismic imaging faces several limitations when it comes to detecting near-surface faults. The most severe are resolution constraints originating from low frequency content and nodal recording system. Lack of low frequencies due to small seismic sources used in near-surface studies limits the accuracy in obtained results at certain depths and makes it difficult or impossible to use the most advanced full waveform inversion techniques [41]. The resolution of nodal acquisition is limited due to receiver spacing, which is a tradeoff between imaging of smaller scale shallow features and deeper structures [42]. The other limitation is related to near-surface complexities and wave-propagation physical limitations. It is challenging to image small-scale features related to weathering and water saturation, but also vertically layered strata that might exist in fault zones. Also, the MASW technique, which is widely used in engineering applications, may not be effective in fault zones with strong lateral heterogeneities and deeply buried structures [43]. Fault imaging in seismic data is inherently constrained by geological and geophysical factors, including horizon truncation, fault dip, geometry, connectivity, and strain characteristics within relay ramps. These geological constraints, combined with limitations in resolution and velocity control, can complicate accurate fault interpretation, particularly within zones of complex architecture [44]. However, integrating surface outcrop data provides a refined geometric model, linking detailed surface features to subsurface structures. This approach mitigates interpretational challenges and supports conditioning of seismic data, as outcrops offer visible structural details that improve subsurface mapping accuracy [45]. Quality control procedures throughout each processing step ensured enhanced data quality in the final seismic stack, with notable improvements in both the signal-to-noise ratio and amplitude spectrum. These enhancements enabled clearer detection of near-vertical faults and improved subsurface resolution. This outcome highlights the potential of affordable, high-resolution seismic profiling as a valuable tool for structural imaging, supporting geological interpretation in academic research and exploration settings [46]. In this study, the field experiment employed a 5 m spacing for geophones and shot points, which, while adequate for general reflection imaging to depths of several hundred meters, limits the resolution needed for resolving finer variations in shallow tomography. This constraint was evident when imaging shallow layers at c.a., the first 5 m, and intricate fault architecture. A denser, 2 m spacing would provide higher resolution at shallow near-surface, facilitating more detailed reflection imaging to enhance the tracing of near-vertical faults and subtle structural changes [47]. The data further reveal (Figure 7) that the fault system within the study area is more intricate than previous interpretations suggested, challenging the notion of the Holy Cross Fault (HCF) as a single structure (see Figure 1). Instead, seismic results suggest the HCF exists within a broader fault zone comprising multiple intersecting fault strands and diverse fault geometries.