Geophysical and geochemical multi-method investigations for reconstructing subsurfaces, alluvial sedimentology, and structural geology (Tiber valley, Rome)

Geophysical and geochemical methods were applied to detect the subsurface setting of an Upper Pleistocene-Holocene fluvial incised-valley where a travertine body intercalates between alluvial deposits of the Tiber river (central Italy), at Prima Porta (close to Rome). This study allowed us to provide more information regarding the local stratigraphic architecture and structural features, as a reference analogue to similar settings: i.e., hard (stiff) lithic travertines buried below fine and loose alluvial plain covers. Two Electrical Resistivity Tomography (ERT) profiles, interpreted and calibrated using previously collected litho-stratigraphic data from a borehole, identified a massive body, with a relatively high resistivity that correlates with the travertine deposit of Prima Porta. In addition to ERT, ambient noise measurements, processed with the HVSR technique and 2D array, and seismic refraction tomography were carried out; HVSR data were highly consistent with ERT results and allowed to discriminate between the travertine body and the silty-sand channels and overbank deposits, which were attributed to the Tiber river's evolution during Upper Pleistocene-Holocene. Finally, the presence of cracks/fractures could be inferred, as suggested by slight polarisation effects recorded in the HVSR results and soil-gas anomalies.