Petrophysical joint inversion of seismic refraction, resistivity, and time-domain induced polarization tomographic data for quantitative imaging of coastal aquifers

The characterization of aquifers is critical for managing freshwater resources threatened by urbanization, agriculture, and climate change. Traditional geophysical techniques, such as electrical resistivity tomography (ERT) and seismic refraction tomography (SRT), provide insights into subsurface structures but can be limited by resolution and interpretational ambiguities. This study introduces a novel approach that combines ERT, SRT, and time-domain induced polarization (TDIP) data in a petrophysical framework, including a direct transformation model (numerical three-phase model [N3PM]) and a comprehensive petrophysical joint inversion scheme. By integrating these complementary data sets, our method enhances the high-resolution imaging of coastal aquifers, enabling more accurate identification of the water table, porosity, and salinization. This approach was tested on a synthetic example and two field sites in the Pontina Plain, Italy. Results demonstrated that N3PM allows for a fast petrophysical screening where prior knowledge is available and the contribution of surface conduction is properly acknowledged, whereas the joint inversion, particularly with the inclusion of TDIP, ensured the reliable characterization of aquifer layers, capturing fine-grained and saline-impacted zones. This approach advances the noninvasive, quantitative assessment of aquifers, offering a valuable tool for groundwater management in coastal regions.