GNGTS 2019 - Atti del 38° Convegno Nazionale

612 GNGTS 2019 S essione 3.2 Bortolami G.C., Maffeo B., Maradei V., Ricci B., Sorzana F.; 1976. Lineamenti di litologia e geoidrologia del settore piemontese della Pianura Padana. Quaderni dell’Istituto di Ricerca sulle Acque, 28 (1), 3-37, Roma. Carraro F. (Ed.); 1996: Revisione del Villafranchiano nell’area tipo di Villafranca d’Asti. Il Quaternario It. Journ. Quatern. Sc., 9(1), pp. 119. Dela Pierre F., Piana F., Fioraso G., Boano P., Bicchi E., Forno M. G., Violanti D., Clari P., Polino R., Balestro G. and D’atri A.; 2003: Foglio 157 “Trino” della Carta Geologica d’Italia alla scala 1: 50.000. APAT, Dipartimento Difesa del Suolo, Roma. Forno M.G., Gattiglio M., Comina C., Barbero D., Bertini A., Doglione A., Irace A., Gianotti F., Martinetto E., Mottura A., Sala B. (2015). Stratigraphic and tectonic notes on the Villafranca d’Asti succession in type-area and Castelnuovo Don Bosco sector (Asti reliefs, Piedmont). Alpine and Mediterranean Quaternary, 28(1), 5-27. Liborio G., Ragni U., Schiavinato G.;1967: Foglio 44 “Novara” della Carta Geologica d’Italia alla scala 1:100.000. IIa ed., Serv. Geol. It., Roma. Lualdi M., Zanzi L., Binda L.; 2003: Acquisition and processing requirements for high quality 3D reconstructions from GPR investigation. Proceedings of the International Symposium on Non-Destructive Testing in Civil Engineering, September 16-19, Berlin, pp. 13. Lualdi M., Zanzi L., Sosio G.; 2004: Metodologia di rilievo georadar 3D per applicazione archeologiche. Atti del 23° Convegno Nazionale GNTS. Vol. 23, 194-200, Ed. Mosetti Tecniche Grafiche, Roma, 14-16 dicembre 2004. Lucchesi S.; 2001: Sintesi preliminare dei dati di sottosuolo della pianura piemontese centrale. Riv. Ass. Geor. Amb., GEAM, 28(2-3), 115-121. PASSIVE SEISMIC SURVEYS IN SUPPORT OF STRATIGRAPHIC CHARACTERIZATION OF A LANDSLIDE BODY D. Barbero 1 , A. Maroni 2 , S. Peyrot 3 1 Geological, Geotechnical and Geophysical Office Dr. Diego Barbero, San Martino Alfieri, Italy 2 Geology Student, University of Turin, Italy 3 Geologist, Freelance professional, Italy Introduction. The passive seismic technique HVSR (Horizontal to Vertical Spectra Ratio) shows a large diffusion in the engineering geology as non invasive, fast and low-cost underground explorative tool. This technique is largely used in seismic microzoning applications to estimate the shear wave velocity (Vs30 parameter, see Castellaro et al. , 2009, now Vs, eq according to NTC2018) and in the engineering filed to measure the resonance frequency of buildings (Gallipoli et al. , 2001; Castellaro et al. , 2005). Recent studies point out the capability of this technique to deduce information about stratigraphy, starting from the resonance frequencies of sedimentary layers and, more generally, the thickness of a sedimentary cover overlying bedrock or bedrock like (Castellaro et al. , 2005; Hinzen et al. , 2004; Ibs-von Seth and Wohlenberg, 1999) or to detect buried morphologies (Grippa et al. , 2011). The aim of this study is to show an application of the HVSR technique, as stratigraphic tool, to map a triggering of a older landslide body occurred in 1982 in the hills of the southern Piedmont (Asti Province). The triggering of this landslide was due to exceptional meteoric events occurred in March 2015 causing a remarkable rise of water levels of the rivers in the Tanaro Basin with associated flooding and landslides. The landslide body analyzed in this study correspond to a difficult case because of the slide surfaces are shaped in the same litotype (Lugagnano Clay): they consist of the overlap of reworked clay layers involved in the landslide reactivation. The presence of these slide surfaces is highlighted by strong impedance contrasts (high peaks) corresponding to poor mechanical coherence of the formations; conversely, the gradual increase of shear waves with depth indicates good mechanical characteristics of the substrate formation.