GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.2 575 Fig. 1 – Map showing the position of geophysical surveys completed at the Mount Vallatrone experimental site. UTM 33 coordinates are shown at Map edges. Contour interval is 20 m. thickness and shallow structure of pyroclastic deposit from multiple geophysical methods, Mount Vallatrone, southern Italy P. Tedesco, L. Guerriero, R. Maresca, F. Guadagno Dipartimento di Scienze e Tecnologie, Università degli Studi del Sannio, Benevento, Italy Introduction. Most of the carbonate relief of the Campania Region (southern Italy) are mantled by pyroclastic deposits originated during eruptions of the Somma-Vesuvius and Phlegraean Fields volcanic centers. Such deposits, commonly characterized by an alternation of ashy and pumiceous layers, have been frequently involved in high velocity flow/avalanche instabilities causing important loss of life and extensive damages (e.g. Guadagno et al. , 2005; Revellino et al. , 2013) to properties and infrastructures. Their physical and stratigraphic characteristic, their geometry and spatial continuity and the morphology of the affected slope have been recognized to control the location of the source zone and the triggering mechanisms (e.g. Guadagno et al. , 2005; De Vita et al. , 2013). Especially, the thickness of the deposit and its internal architecture seems to be a key predisposing factor for the development of these instabilities (De Vita et al. , 2006, 2013) and their knowledge is essential for the analysis of landslide susceptibility. On this basis, in this work, we experiment multiple geophysical methods to characterize the geometry and the stratigraphic characteristics of pyroclastic deposits covering the northern slope of Mount Vallatrone in Campania region (southern Italy). Especially, for our analysis we used HVSR measurement, MASW and GPR surveys. All of the surveys were completed along a section where a detailed stratigraphy, reconstructed using data from a hand excavated borehole, was available. This improve our experimentation allowing a comparison/integration of the results. Geologic setting. The experimentation site is located along the northern slope of the Mt. Vallatrone (Fig. 1) a relief of the Avella-Partenio Mountains in southern Italy. Such mountains are formed of Jurassic-Cretaceous carbonate-dolomitic rocks (Sgrosso,1965; D’Argenio et al. , 1970). Many fractures and NW-SE and NE-SW trending normal faults are present (Ippolito et al. , 1973). Structural evolution, connected to Quaternary tectonic phases, as well as geomorphological degradation processes, generated internal depressed areas into carbonate ridges. Frequently, several meters of air-fall pyroclastic deposits, characterized by an alternation of ash and pumice layers, overlie the calcareous slopes. Thedistributionofpyroclastic deposits is not homogeneous, but follows the original dispersion axes of the various volcanic eruptions (Rolandi et al. , 1993). Stratigraphy of pyroclastic deposits is not frequently exposed and, for our investigation, was investigated hand-excavating a borehole (Fig. 1). Such borehole reveals the stratigraphy down to a depth of about 6 m (Fig. 1). It