GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 19 low P-velocity is recognizable from 30 to 50 m depth along the profile, which was interpreted as fractured material confined within two more compact blocks (dashed black line). Two ERT profiles were also performed, the first one is a 2D ERT profile acquired along the road that runs from west to east, whereas the second one is a quasi-3D ERT profile. The 2D ERT profile shows a generalized low resistivity of the terrain (10 1 < ρ < 10 2 Ωm). This would find correspondence with the stratigraphy of the area characterized by a marine silty-clayey deposit below a thin layer of weathered volcaniclastic rocks, as revealed by some geognostic boreholes (Ferrara, 2010). At about 5 m depth, the portion between 30 and 50 m, is characterized by the lowest resistivity values (black-dashed line in Fig.3b, which encloses a zone with ρ < 5 Ωm, blue circle) and it can be interpreted as a layer of water-saturated material. The GPR profile shows some truncations and offsets of the reflections, interpreted as fractures along a fault plane. A change in the electromagnetic facies is recognizable between the progressive distances of 35 and 50 m (the yellow area in Fig. 3c). This was interpreted as a physical separation between the western and eastern zones, characterized both by high reflectivity and by high absorption of the electromagnetic signal. Furthermore, the electromagnetic facies in the westernmost part of the radargram can be correlated with the shallow zone having higher velocity in the SRT (Fig. 3c), where the anomalies found are likely associated with buried structures. The magnetic survey revealed two main bipolar anomalies: a smaller one, about 10 m wide, with amplitude of about 60 nT, and a larger one (40–45 m wide) with amplitude of about 570 nT (Fig. 3 d). The first one is probably due to a buried pipe, while the second one is ascribable to a geological source. Geochemical investigation. Soil CO 2 effluxes were measured using the accumulation chamber method, which consists of measuring the rate of increase of CO 2 concentration inside a cylindrical chamber open at its bottom and placed on the ground surface (Parkinson, 1981). The change in concentration during the initial measurement is proportional to the efflux of CO 2 (Tonani and Miele, 1991). Anomalous diffuse CO 2 emissions at Mt. Etna are caused by deep magma degassing through tectonic lines at lithospheric and shallow levels. The spatial distribution of CO 2 effluxes revealed three main areas of anomalies at the site. The first one, located to north, displays anomalies aligned with an existing fault line belonging to the Timpe system. The second area, located to south, seems correlated to a buried ~NE-SW oriented fault. Finally, the third area, located in the central part, shows anomalies of lower intensity than the previous, and are scattered over a larger surface, around the emission points of slightly thermalized sulphurous waters. In this case, soil gas anomalies may represent degassing of deep CO 2 exsolved from a thermal aquifer along its underground path. Continuous monitoring of bubbling gases emitted in a thermal well have been performed in order to better identify the components of hydrothermal system and to assess variations in chemical composition in the short period. Cromatography Monitoring Station (CMS) offers a high frequency of automatic gas analysis (our gap was 30’) allowing to identify two anomalous degassing. At the end of January, the chemical composition changed drastically with detectable concentration of H 2 S and ethane associated with very high concentration of CH 4 (70%) without sensible variations of CO 2 . The correlation among CH 4 and H 2 S and ethane suggest that the hydrothermal end member (methane dominant) has a mix with a superficially component more rich in CO 2 . Finally, we measured the temperature of the thermal waters every 15’ by using a Tinytag datalogger. The data showed regular daily fluctuations and a seasonal trend. Instead, the hydrothermal fraction is mainly composed of low-enthalpy gases (CH 4 ) that do not affect significantly the water temperature; therefore, any future ascent of hot fluids would be immediately emphasized. Conclusions. The integration of geophysical and geological data allowed the recognition and characterization of coseismic faulting affecting the archaeological site of Santa Venera al