GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 13 Lombardi and Voltattorni, 2010). In fact in seismically active zones anomalous concentrations of various minor and trace gas species (i.e., CO 2 , Rn, H e , H 2 , CH 4 ) are a widely observed process (e.g., Ciotoli et al. , 2007, 2014; Voltattorni et al. , 2012). The degassing process, occurring as advective migration of free gas phase in fractured rock volumes at depth, indicates that active faults are characterized by high permeability, and thus act as preferential conduits in the crust (Ciotoli et al. , 1998, 2007, 2013, 2014; Toutain and Baubron, 1999; Annunziatellis et al. , 2008). An integrated approach, based on the search for geomorphological and geochemical indicators of faults showing evidence of late Quaternary activity at the surface is used in our study, which is being carried out in the framework of the INGV-DPC 2014-15 Progetto S1, and aims at providing new data on the active tectonics of the area including the southern Matese ridge and adjoining valleys (Fig. 1). The Matese ridge falls in the epicentral area of strong historical earthquakes, the most destructive, with X-XI MCS intensities and Mw from 6.7 to ≥ 7, occurred in 1349, 1456, 1688 and 1805 (e.g., Gasperini et al. , 1999; Galli and Galadini, 2003; Di Bucci et al. , 2005; Fracassi and Valensise, 2007; Locati et al. , 2011; Rovida et al. , 2011; Fig. 1a). Such strong earthquakes affected the area with coseismic ruptures and a large number of secondary geological effects, including landslides, sinkhole collapses and changes of discharge rate and chemical properties of major springs (e.g., Porfido et al. 2007; Di Bucci et al. , 2005, 2006; Fracassi and Valensise, 2007; Galli and Naso, 2009; Del Prete et al. , 2010). The seismogenic sources of the 1805, 1688 and 1349 earthquakes according to the DISS Working Group (2010; and references therein) are shown in Fig. 1b. In the last decades, the area has been affected by low-magnitude background seismicity characterised by both sparse earthquakes and seismic sequences (Milano et al. , 2005; Chiarabba et al. , 2011; Fig. 1a). From the end of 2013 to the early 2014, the area has been struck by a further seismic sequence. The epicentre of the ML=4.9 main event, which has occurred on 29th December and has been characterised by a normal faulting mechanism, has been localised in the SE part of the Matese ridge (http:// cnt.rm.ingv.it/tdmt.html ; Fig. 1b), i.e. between those which are acknowledged as the main seismogenic structures, and in area in which no fault strand showing evidence of recent activity had been mapped to date (e.g., Cinque et al. , 2000). This points to the need of focussing the investigation both within and around the Matese ridge in order to better define the overall surface deformation scenario. In this paper we present new, preliminary data from the southern Matese ridge area, with a particular focus on those providing evidence of active tectonics in the Colle Sponeta area (Fig. 1b). Geological setting. The study area is located in the Campania-Molise sector of the southern Apennines. The southern Apennines is a NE-directed fold and thrust belt formed in Miocene to Quaternary times, with thrusting coexisting with back-arc extension in the southern Tyrrhenian basin since the late Miocene (e.g. Cinque et al. , 1993). Back-arc extension caused formation, since the Early Pleistocene, of large peri-Tyrrhenian grabens (e.g., Caiazzo et al. , 2006) in some of which volcanism developed since the Middle Pleistocene (e.g., Radicati Di Brozolo et al. , 1988). Thrusting ceased in the early Middle Pleistocene, and a new tectonic regime with NE- SW oriented maximum extension was established in the chain (e.g., Cello et al. , 1982; Cinque et al. , 1993; Montone et al. , 1999; Patacca et al. , 2008). The structures related to this regime include dominantly extensional faults that postdate and dissect the thrust belt (e.g., Cello et al., 1982; Ascione et al. , 2013). Based on fault-plane solutions, normal faults also control seismogenesis in the mountain belt, which is affected by low to moderate events punctuated by strong earthquakes, mostly following the chain axis and originating on NW-SE trending faults (e.g., DISS Working Group, 2010). In the study area, tectonic units of the fold and thrust belt are composed of Mesozoic- Tertiary successions covered by Neogene foredeep basin deposits. These consist, from the top, of carbonate successions (Apennine Platform, outcropping in the Matese ridge), pelagic basin