GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 452 HIGH-RESOLUTION ERT IMAGING OF CO 2 DEGASSING ALONG ACTIVE FAULTS ON THE SOUTH-WEST FLANK OF THE MATESE MTS. (SOUTHERN APENNINES) R. Salone 1 , C. De Paola 1,2 , L. Ferranti 1 , R. Di Maio 1 1 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università di Napoli Federico II, Napoli, Italy 2 SOCOTEC Italia s.r.l., Lainate, Milano (Italy) Introduction The emission of gas along active faults represents the shallow manifestation of a gases migration path from a deep natural source, and it indicates that the fault zones are characterized by high permeability, acting as drains in the crust (Annunziatellis et al., 2008; Faulkner et al., 2010). When these gases reach the surface, they are usually discharged into the atmosphere from small areas known as gas vents . Understanding gas migration along faults is a key scientific problem in many geoscience researches, such as geothermal exploration and geohazard assessment. The growing attention to this issue is related to the potential impact of the natural CO 2 release on human health and ecosystems, groundwater quality, soil mineralogy and CO 2 concentrations in the atmosphere. In this framework, for the purposes of the gas hazard assessment, the geophysical prospecting methods are successfully and increasingly applied for the identification of active faults and for the detection and monitoring of CO 2 degassing along them. In particular, over the last decade, geoelectrical surveys performed by electrical resistivity tomography (ERT) technique have proven to be among the most appropriate prospecting methods to detect spatial distributions of carbon dioxide (Kiessling et al., 2010; Schmidt-Hattenberger et al., 2011; Bergmann et al., 2012; Furre et al. 2017), whose emission in non-volcanic areas is essentially controlled by fractures, faults and fault damage zones. Indeed, the ERT technique is able to identify the areas of influence of the gas vent as either conductive and resistive anomalies, depending on the geological environment and the physical, chemical and biological conditions of the investigated risk areas (Arts et al., 2009; Pettinelli et al., 2010; Byrdina et al., 2014). In this work, we present the results of a high-resolution electrical resistivity tomography survey aimed to identify the active fault zones that control the release of significant CO 2 flows in the Ailano area (Matese Mts., Southern Italy). Geological Background The Ailano survey area is located in the southwestern sector of Matese massif (Southern Apennines), where tectonic units of the fold and thrust belt are composed of Mesozoic-Tertiary carbonate successions covered by late Miocene foredeep basin deposits (Fig. 1). The area is characterized by a very high density of CO 2 -dominated natural gas vents (~200 in ~2 km 2 ) that are recognized in the field by the scarce and/or total absence of vegetation, and by bubbling phenomena in the water sources and sinkholes (Ascione et al., 2018). This occurrence is commonly interpreted as an indicator of intense alteration associated with the increase of fluids and correlated to the fluid-rock interactions that occur at depth preferentially along active faults (Annunziatellis et al., 2008; Santo et al., 2011). Indeed, these gas emissions are located in a region that is dismembered by a large number of faults. In particular, the alignments of the gas vents are consistent with the directions of some fault segments active during the Late Quaternary (Ascione et al., 2018).