Imaging fault-controlled karst systems through integrated Resistivity and IP inversion in the Umbria-Marche Apennines, Piani di Montelago (Sefro, MC)

Fault-controlled karstic systems hosted in carbonates strongly influence groundwater flow and morphological evolution, including the development of associated basins. Characterizing the geometry of the karst system and related sedimentary basins may contribute to modelling the groundwater system, determining hazards related to collapse, and understanding the relationship with associated geological structures. However, subsurface imaging and geophysical characterization may be challenging due to the depth of the hosting rocks, the presence of saturated layers, and the dimensions of the area affected by the systems. In the case of large and morphologically complex areas, 3D deep full-waveform geo-electrical surveys using wireless devices help to overcome the limitations of conventional small-scale electrical surveys. In particular, the ability to generate integrated Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) models has proven effective in imaging karst features, allowing the detection of cavities and structural complexity.

The Piani di Monte Lago basin, in the Umbria–Marche sector of the Central Apennines, is an intramountain karst–tectonic basin characterized by the development of seasonal lakes and presents a poorly understood karst system with fast water discharge. Its evolution has been shaped by karst processes, with poljes and active ponor drainage developing under the combined influence of tectonic deformation, lithological contrasts, and Pleistocene geomorphological changes.

This work aims to characterize fracture zones and karst features through a combined application of deep ERT and Induced Polarization (IP). The approach integrates acquisition, processing, modelling, and geological interpretation to achieve a more accurate subsurface image in this structurally complex setting.

The survey was conducted using the FullWaver® wireless system (IRIS Instruments), deploying 15 dual-channel receivers and a 5-kW transmitter across an 800 × 800 m area. Flexible quadrupole configurations and dipoles up to 1000 m enabled investigation depths of about 200 m, while GPS synchronization ensured precise time-domain measurements of resistivity, IP, and self-potential, with a timing accuracy of 250 µs.

The generated models, constrained by geological and topographic data, reveal sharp resistivity contrasts between the carbonate substratum and overlying lacustrine deposits. IP variations highlight fracture zones and possible buried structures that control hydraulic connectivity. These results provide new insights into the structural influence on karst development and clarify subsurface drainage patterns. By integrating geophysical inversion with geological constraints, this approach reduces uncertainty and refines 3D models in structurally complex carbonate settings. The findings have direct implications for groundwater resource management, environmental assessment, and land-use planning in tectonically active regions.