Geochemical and radiometric profiles through an active fault in the Sila Massif (Calabria, Italy)

Abstract

Geochemical and geophysical surveyswere carried out in the Cagno valley (Sila massif, central-northern Calabria, Italy) to investigate the gas bearing properties of a seismogenic fault (Lakes Fault, LF), discovered by paleoseismological analysis. Soil gas measurements (N2, O2, Rn, CO2, CH4 and light hydrocarbons) and exposure to γ radiations were performed along two detailed profiles (about 150 m long), trending almost parallel to a trench crossing the LF. The highest values of Rn, γ radiation, CO2, CH4 and light hydrocarbons were detected in the area around the LF and 100 m far away. In the central part of the profiles, where a hanging valley is present, geo-gas distribution is likely controlled by both lithology (colluvial deposits and peaty silt deposits, characterized by mediumto low permeability) and the presence of a local cold aquifer. In particular,water table influences the circulation of the gas species in the sub-surface environment, aswell as their distribution at the surface by playing a sort of sealing effect for the gasmigration. In the area located about 100mwestward of the fault, characterized by soils originated from altered granodiorites, the occurrence of a previously unknown blind fault is supposed. The multidisciplinary approach of this work allows to better understand the relationship between geochemical and geophysical analyses linked to migration processes of deep fluid through preferential leakage pathways providing some hints on the spatial influence of active tectonic.