Imaging near-surface geometry of mud volcanoes: a multi-method geophysical study from Monteleone di Fermo (Marche Region, Italy)

Mud volcanoes are key geo-environmental features, particularly in central Italy, where their origin is linked to the interaction between tectonics, fluid migration, and high sedimentation rates. In the Monteleone di Fermo area (Marche Region), these structures are aligned with active thrust faults and anticlines of the Marche–Abruzzi system. Despite their relevance as geo-heritage sites and their potential as geohazard indicators, a significant gap persists in the knowledge of their subsurface architecture. Previous studies have focused primarily on compositional aspects and geomorphological descriptions, proposing contrasting triggering and fluid transport mechanisms.This work constitutes a pioneering study in the geophysical characterization of the Monteleone di Fermo mud volcanoes, aiming to define their near-surface geometry and distribution. A multi-parametric approach was applied, integrating full-waveform 3D Electrical Resistivity Tomography (ERT) and 2D seismic refraction tomography (P- and S-wave velocities). Results show distinctive geophysical signatures associated with the system’s saturation state and mud accumulation. The 3D ERT imaging, reaching effective depths of nearly 100 m, shows a slight resistivity contrast between mud bodies (ρ = 10–15 Ω·m) and the hosting clay-rich deposits with lower resistivity (ρ = 8–10 Ω·m). Seismic tomography reveals a marked contrast between the mud edifice and the hosting sediments. In particular, Poisson’s ratio increases (ν > 0.45), indicating the presence of fully saturated muds intruding the clay-rich sediments (ν = 0.35–0.40).These results demonstrate both the feasibility and limitations of full-waveform geo-electrical data for deep 3D resistivity imaging in clay-rich sediments, testing the detectability of mud-volcano structures under low resistivity-contrast conditions. The study further benchmarks sensitivity against complementary seismic indicators (Vp/Vs and Poisson’s ratio), supporting a multi-physics strategy for resolving fluid-migration pathways in challenging near-surface settings.