Advanced Boundary Analysis techniques as a tool to decipher volcano-tectonic setting of the Campi Flegrei caldera

Faults are essential structures in the Earth's crust, playing a key role in regulating subsurface fluid flow and driving crustal deformation. In volcanic regions, they facilitate the migration of magma and fluids, significantly influencing volcanic processes and associated deformation patterns. Understanding the interplay between deformation patterns, subsurface heterogeneities, and fault structures is critical for accurately interpreting local volcanic dynamics, situating them within broader geodynamic frameworks, and assessing potential hazards. Boundary analysis techniques, traditionally applied to potential field data, are effective tools for investigating subsurface heterogeneities. Key methods include the Total Horizontal Derivative (THD), Tilt Angle of Horizontal Gradient (TAHG), and Normalized Total Gradient (NTG). Among these, THD has proven particularly valuable for detecting deformation sources in volcanic regions. Specifically, at Campi Flegrei caldera (CFc), THD has been applied to gravity and magnetic data as well as InSAR-derived deformation measurements, effectively aiding in the precise identification of the extent of the local volcanic source of deformation. This study integrates boundary analysis techniques (THD, TAHG, and NTG) with seismic tomography results and InSAR deformation data to conduct a comprehensive structural analysis of CFc and surrounding land and marine areas. Using datasets from mid-2021 to mid-2022, we delineate surface and subsurface structures, correlate them with major tectonic trends, and analyze their relation to local seismicity. Seismic tomography data from Giacomuzzi et al. (2024) provide 3D insights into seismic velocity distributions, highlighting crustal heterogeneities and structural weaknesses. To enhance interpretation, Total Horizontal Derivative (THD) emphasizes shallow features like faults and lithological contacts, while Tilt Angle of Horizontal Gradient (TAHG) and Normalized Total Gradient (NTG) analyze vertical deformation from InSAR data, improving sensitivity to deeper structures and minor heterogeneities. These techniques balance resolution and minimize noise, making them particularly suited for analyzing high-resolution deformation fields. To validate these techniques, we also conducted a testing phase using synthetic simulations. Our results reveal a regionally coherent yet intricate deformation pattern, consistent with the trends outlined in existing volcano-tectonic maps. This study enhances understanding of the Campi Flegrei caldera (CFc) and highlights the broader applicability of advanced boundary analysis techniques for volcano-tectonic investigations. By integrating seismic and deformation datasets with sophisticated analytical approaches, it offers valuable insights into the spatial and functional relationships between crustal heterogeneities and deformation dynamics, establishing a foundation for future research in active, densely populated regions.