New insights from geophysical UAV sensing of the Mefite d’Ansanto site (Southern Italy)

Abstract Mefite d’Ansanto (Southern Apennines, Italy) is one of the largest known non‑volcanic CO 2 degassing sites worldwide. The degassing process observed here is widely recognized as the surface manifestation of the interaction between mantle-derived CO 2 and a complex shallow fracture network. The hazardous conditions surrounding the main emission vents limit conventional ground-based geophysical surveys, making an accurate reconstruction of the geometry and spatial distribution of the local fracture system particularly challenging. Here, we present the first Unmanned Aerial Vehicle (UAV)‑based geophysical investigation of this inaccessible and unsafe area. Specifically, high‑resolution drone‑borne magnetic measurements are acquired and subsequently analysed through multiscale potential field imaging methods to map subsurface structures. The retrieved magnetic map reveals two different anomalies, both characterized by an amplitude of several tens of nanotesla, and elongated along a NW-SE direction. We then apply the Tilt Angle of the Horizontal Gradient (TAHG) boundary analysis technique revealing a distribution of maxima, whose alignment suggests a N45°W dominant structural trend. This trend is consistent with regional NW-SE trending extensional structures. Subsequently, Multiscale imaging methods consistently locate the magnetized source at shallow depths (~ 25–120 m), also indicating a structurally-controlled source geometry. Our findings delineate and characterize shallow magnetized zones that, as a possible interpretative geological scenario, represent the result of fluid-induced mineralization driven by high permeability within the local fracture network. The results provide direct geophysical evidence of the influence of shallow structures on fluid migration pathways in the shallow crust and demonstrate the effectiveness of UAV-based methods for investigating inaccessible and hazardous geological systems.