GNGTS 2022 - Atti del 40° Convegno Nazionale

468 GNGTS 2022 Sessione 3.2 THE SALSE DI NIRANO MUD VOLCANIC FIELD: NEW GEOPHYSICAL RESULTS AND THEIR HYDROGEOLOGICAL IMPLICATIONS A. Falconieri 1 , D. Patella 2 , A. Piombo 3 , G. Romano 2 , A. Siniscalchi 2 , A. Tallarico 2 1 GEOPROSYS s.r.l., Bari, Italy 2 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari Aldo Moro, Bari, Italy 3 Dipartimento di Fisica e Astronomia “Augusto Righi”, Alma Mater Studiorum - Università di Bologna, Bologna, Italy The Nirano Salse is an active mud volcanos belt located in the northern Apennine foothills near Fiorano Modenese. The belt consists of four cone shaped emission centres, aligned along a N55 direction with basal diameters of about 4-5 m and heights of 2-3 m. Although the area has been widely investigated since the Regional Natural Reserve of Nirano Salse was established in 1982, the subsurface structure is still not well resolved in depth leaving open questions on the feeding related dynamics of the volcanos. Recent studies (Giambastiani et al., 2021) suggest that gas from a deep reservoir would accumulate in shallow aquifers confined in the first tens of meters of depth and starting point of the conduits forming the mud volcanoes. The features of the fractures system and conduits feeding from the deep source into the shallow aquifers are still unclear. To this aim, in March 2022 a geophysical field survey was performed and two orthogonal Electrical Resistivity Tomographies (ERT) were acquired crossing the whole caldera-like structure at the bottom of which the mud volcanoes are located. The shallow (about 60 m of depth) subsurface structure of Nirano main mud volcanic emission centres was already imaged by the geolectrical studies presented in Lupi et al 2016. In the present investigation, the survey was not limited on mud volcanos area but was extended in order to include, as much as possible, the whole caldera-like structure. The use of a large interelectrode spacing and of a data strategy collection based on the application and integration of different geoelectrical arrays (Pole-Dipole, Dipole-Dipole, Wenner and Wenner- Schlumberger) allowed us to gather information on the electrical property distribution from the surface up to ~ 300 m b.g.l.. The integrated interpretation of the ERT results, previously acquired geophysical data, geological and hydrogeological results confirm the main outcome of Lupi et al., 2016 in the shallow subsoil portion but also furnish new hints on the subsoil structure at greater dept probably connected with the presence of medium depth source for the Nirano systems. Furthermore, having the survey included also the caldera rims areas, the ERT results help in better define the connections between the surficial hydrogeology of the area and the mud volcanoes activity. Bibliografia Lupi M., Suski Ricci B., Kenkel J. Ricci T. and Fuchs F.; 2016: Subsurface fluid distribution and possible seismic precursory signal at the Salse di Nirano mud volcanic field, Italy. Geophys. J. Int., 204 , 907–917, doi: 10.1093/gji/ggv454 Giambastiani B. M. S., Antonellini M., Nespoli M., Bacchetti M., Calafato A., Conventi M., Dadomo A., Martinelle G., Morena M., Venturoli S. and Piombo A.; 2021: Mud flow dynamics at gas seeps (Nirano Salse, Italy) submitted for publication to Environmental Earth Sciences