GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.2 661 Santilano A., Godio A., Manzella A., Menghini A., Rizzo E, Romano G (2015). Electromagnetic and DC methods for geothermal exploration in Italy, state-of-the-art, case studies and future developments. First Break 33 (8), 81-86 August 2015 Sappa G., Tipologie e distribuzione delle fonti di approvvigionamento idropotabile in Italia, in Ingenio, n.2, Marzo 2013, pp. 1-10 GEOPHYSICAL AND GEODETIC SURVEYS FOR THE CHARACTERIZATION OF THE SANTA BARBARA MUD VOLCANO SUBSOIL (CALTANISSETTA, SICILY): PRELIMINARY RESULTS S. Imposa, S. Grassi, G. De Guidi, G. Patti, F. Brighenti, F. Carnemolla Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università degli Studi di Catania, Catania, Italy Introduction. Mud volcanism is common worldwide, about 1,100 mud volcanoes have been identified onshore (Milkov 2005). Sixty-one mud volcanoes have been identified in Italy, mainly located on thick sedimentary sequences within zones of active tectonic compression. Mud volcanoes are considered pseudo-volcanic manifestations, originating from the presence of natural gases under pressure in the subsurface. These gases tend to rise through preferential migrating pathways due to the presence of permeable rocks and/or lithological discontinuities, carrying water, mud, rock fragments and hydrocarbons as they ascend. This study presents the preliminary results of geophysics and geodetic field surveys involving the Santa Barbara mud volcano area, aimed at characterized its subsoil. The Santa Barbara mud volcano area is located in central sector of Sicily (Fig. 1a), on the eastern outskirts of the Caltanissetta district (Fig. 1b), at about 520 m a.s.l.. Geological and structural framework. On a regional scale, mud volcanoes in active fold- and-thrust belts may occur over wider areas or may cluster along discrete structures, where the generation of overpressures is expected to establish a positive feedback loop allowing for fault movement and mud volcanism. The mud volcanoes in Sicily, are all located along the Sicily Thrust Belt Front (Lavecchia et al., 2007; De Guidi et al., 2015). The Sicilian belt is part of the complex collisional boundary between African and Europe convergent plates. The central sector of Sicily consists of four groups of terrain, three represent tectonic complexes, while the latter consists of piggy-back deposits deposited on the back of the three tectonic complexes. The geological succession, outcropping in the area of the Santa Barbara Mud Volcano, is represented, form the bottom to the top, by Terravecchia Formation (LowTortonian - Messinian), Calcare di Base (Low Messinian), Trubi Formation (Zanclean), Enna Formation (Piacenzian), Geracello marly clays (Gelasiano) and Lannari sand (Calabrian) (Tortorici et al. , 2014). In particular the mud volcano area is characterized by the clayey member of Trubi Formation, consisting by clays and olistostromic intercalations; Trubi Formation outcropps also southward up to Imera Meridionale River (Fig. 1c). Geophysical and geodetic surveys: methods and data processing To identify the impedance contrast between the material ejected and the rock from which it arises a geophysical survey has been carried out using passive seismic single-station (HVSR) and active seismic (MASW) prospections (Imposa et al. , 2016) (Fig. 1d ). A grid was designed on the Santa Barbara mud volcano area, measuring 110x120 m and with a 10 m spacing between sampling points.