Numerical modelling to identify permeable fractures from geophysical imaging of natural degassing areas. Example from the Matese Fault system (Italy)

Abstract

The characterization of complex geological systems, such as active fault zones and volcanic districts, in terms of volumetric distribution of geophysical parameters is crucial for reconstructing their internal architecture. At the same time, numerical modelling has proven to be a powerful tool for understanding the processes that governs the dynamics of these systems (e.g., fluid and gas migration in faulted rocks, surface subsidence, upwelling of magma or volcanic fluids), as well as their temporal evolution. In this study, we assess the potential of fluid dynamics numerical modelling to identify permeable structural discontinuities from geophysical images of the hypothesized fault/fracture systems that may favour the upwelling of fluids and gases from deep sources to the Earth's surface. The proposed approach is tested in a non-volcanic CO₂ degassing area located on the SW margin of the Mt. Matese (Southern Apennines, Italy), where a previous geoelectrical survey, consisting of high-resolution 3D electrical resistivity tomography and self-potential measurements, was properly integrated with geological and geochemical data. This integration enabled the identification of potential shallow discontinuities (i.e., faults and fractures) that could facilitate fluid and gas migration toward the surface. Numerical simulations modelling the physical processes likely occurring within the imaged system successfully identified fracture networks that may serve as conduits for soil gas migration. Our proposal provides new insights into fault structures and preferential fluid flow paths, which holds promise for the understanding of various geological phenomena, such as geothermal activity, crustal earthquakes, natural gas migration, and anthropogenic CO₂ geological storage.