GNGTS 2014 - Atti del 33° Convegno Nazionale

14 GNGTS 2014 S essione 1.1 successions (Molise-Sannio Basin, outcropping to the N and E of the ridge), and the buried Apulian platform carbonates (Mazzoli et al. , 2000). The thrust pile is dissected by NW-SE extensional structures and E-W trending high-angle faults generally showing left-lateral activity overprinted by either dip-slip or oblique right-lateral motion associated with reactivation during the Middle Pleistocene to Present- tectonic regime (Mazzoli et al. , 2000, and references therein). The area including the southern Matese ridge and adjoining valleys is affected by several extensional faults showing geomorphological-stratigraphical evidence of activity during the late Quaternary. These include a dense net of minor (few km long) faults, mostly with NW-SE, E-W and N-S trends, and some major (tens of km long) extensional fault zones with overall WNW-ESE trends (Cinque et al. , 2000). The main one of the latter structures bounds towards the NE the middle Volturno river basin (location in Fig. 1b), in which the top of the carbonates is lowered below the sea level (Corniello and Russo, 1990). A further main structure is the ≈ 20 km long Pozzilli–Capriati (Brancaccio et al. , 1997), or Aquae Iuliae fault (Galli and Naso, 2009). This fault zone recorded repeated surface ruptures during the late Holocene, with the last one being associated with the Mw ≈ 6.7, 1349 earthquake (Galli and Naso, 2009). To the seismic shaking of this event has been associated the formation of karst collapse sinkholes in the Telese area (Del Prete et al. , 2010). Indeed, the Matese ridge southern boundary is characterised by several karst collapse sinkholes, particularly clustered around Telese and Pratella (location in Fig. 1b). Such phenomena are interpreted as the response to intense dissolution associated with the rise of deep-seated fluids along active faults (Santo et al. , 2011). Worthy to note, both the Pratella and Telese areas are characterised by mineral springs (Corniello et al. , 1999), with the chemical composition of the Telese springs being affected by deep seated inputs along lithospheric faults (Italiano et al. , 2000). The Colle Sponeta area (Fig. 1b) is located in the hanging wall block of the Aquae Iuliae fault, in the SW part of Prata Sannita Quaternary lacustrine basin. It is characterised by a hilly landscape formed in intensely weathered fine-grained alluvial and pyroclastic deposits (Sinno, 1966), which can be related to the older one of the Middle Pleistocene terraced alluvial successions filling the Prata Sannita basin. Materials and methods. In the area of the southern Matese ridge, geomorphological, structural and soil gas surveys are being carried out with the aim of identifying the spatial distribution, the gas bearing properties and the fault zone architecture of faults showing evidence of activity during the late Quaternary. Meso-structural data have been collected in the study area, to constrain the kinematics of the extensional system. Geomorphological analysis of detail scale (1:5,000 CTR maps) topographic maps has been carried out in order to detect classical geomorphological indicators of vertical surface displacements, e.g. rectilinear scarps/ slope breaks and drainage net anomalies. Soil gas survey has been performed in a small area of about 0.7 km 2 located in the Colle Sponeta area (Fig. 1b). A total amount of 233 samples were collected randomly in the study area, which has been selected based on the presence of: • a N-S trending, up to about 8 m high and about 1 km long, E-facing scarp (hereinafter, Colle Sponeta fault scarp; Figs. 2a and 2b); • a large sinkhole (diameter of about 10 m), characterised by strong bubbling due to a free gas phase upwelling (Fig. 2c); • small-sized holes following the toe of the Colle Sponeta fault scarp, associated with bubbling gas in the groundwater; • dead small animals, probably killed by the high CO 2 content above the shallow soil (see next Chapter). Soil gas samples have been collected using a 6.4 mm, thick-walled, stainless-steel tube onto which steel cylinders are welded to act as pounded in the soil at a depth of about 0.6-0.8 m by using a co-axial hammer (Ciotoli et al. , 1998; Beaubien et al. , 2013). ��� ���� �������� ����� The used sampling depth is sufficient to avoid the in uence of in ltrating atmospheric air (Hinkle, 1994). Samples have