GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 107 the past years, threatening the stability of the rock cliff, as well as the static of the cultural heritage site. From the analysis and the interpretation of the seismic noise, it is clear that the adopted geophysical methodology allows highlighting the presence of a different degree of fracturing in the rock mass. Indeed, it is function of the spectral response. These results, however confirmed by the stratigraphy obtained by mechanical drillings, allow us to say that the Convent of Friars Minor stands on a fairly fractured area and the resonance frequency has values ​of 4 Hz (S2 and S3) and 41.88 Hz (S1). Geostructural analysis pointed out the presence of several discontinuity systems. One of them shows an orientation matching with the direction of the NE-SW main fault system. Geomechanical properties of the rock mass are to be considered poor, according to the RMR classification. Moreover, stability analysis highlighted a widespread instability, with planar sliding and wedge as possible failure mechanisms. The limit equilibrium analysis led to the calculation of FS whose values are lower than 1 both in static and pseudostatic conditions. Furthermore, the main instability conditions are related to the southeastern portion of the surveyed slope, where several karst caves are also present. Acknowledgments. This paper was undertaken with the financial support of the University of Catania (PRA n. 20104001082, Scientific Supervisor: S. Imposa). References Amorosi A., Castellaro S., Mulargia F.; 2008: Single-Station Passive Seismic Stratigraphy: an inexpensive tool for quick subsurface investigations . Geoacta, 7 , pp. 29-39 Azzaro F., Barbano M.S.; 2000 : Analysis of seismicity of Southeastern Sicily: proposal of a tectonic interpretation. Annali di Geofisica, 43 (1), pp. 1-18 Barbano M.S., Pappalardo G., Pirrotta C., Mineo S.; 2014: Landslide triggers along volcanic rock slopes in eastern Sicily (Italy) . Nat. Hazards, 73 , pp. 1587–1607, DOI 10.1007/s11069-014-1160-1 Bieniawski Z.T.; 1989: Engineering Rock Mass Classification , John Wiley & Son, 251 Ghisetti F., Vezzani L.; 1980: The structural features of the Iblean Plateau and of the Mont Judica ares (southeastern Sicily): a microtectonic contribution to the deformational history of the Calabrian Arc. Boll. Soc. Geol. It., 99 ; pp. 57-102 Grasso M., Reuther C.D., Tortorici L.; 1992: Neotectonic deformations in SE Sicily: the Ispica fault, evidence of late Miocene-Pleistocene decoupled wrenching within the central Mediterranean stress regime . J Geodyn., 16 (1/2), pp. 135–146 Grasso M., Pedley H.M., Maniscalco R., Ruggieri R.; 2000: Geological context and explanatory notes of the ‘‘Geological Map of central-southern sector of the Hyblean Plateau’’ . Mem. Soc. Geol., Italy, 55 , pp. 45–52 Hoek E., Bray J.W.; 1981: Rock Slope Engineering , Third Edition, The Institution of Mining and Metallurgy, London, 368 pp. Ibs-von Seht, J. Wohlenberg; 1999: Microtremor measurements used to map thickness of soft sediments. Bulletin of the Seismological Society of America, 89 (1), pp. 250-259 Imposa S., Corrao M., Barone F., Coco G., Occhipinti R., Mozzicato P.; 2010: Geostructural and geognostic survey for a stability analysis of the calcareous cliff of Ispica (Hyblean plateau, southeastern Sicily) . Bull. Eng. Geol. Environ., 69 , pp. 247-256 Imposa S., Corrao M., Mele G., Coco G.; 2014: Geophysical survey of a calcareous cliff in the area of Ispica (southeastern Sicily). Bull. Eng. Geol. Environ, (in press) ISRM; 2007: The complete ISRM suggested methods for rock characterization, testing and monitoring : 1974- 2006. R. Ulusay and J.A. Hudson (eds.), Suggested Methods Prepared by the Commission on Testing Methods, International Society for Rock Mechanics, Compilation Arranged by the ISRM Turkish National Group, Kozan Ofset, Ankara, Turkey, 628 pp. Lentini F., Carbone S., Grasso M.; 1987: Carta geologica della Sicilia sud-orientale . ����� ���������� �������� Scala 1:100.000. S.EL.CA . Firenze Markland J.T.; 1972: A useful technique for estimating the stability of rock slopes when the rigid wedge sliding type of failure is expected , Imp. Coll. Rock Mech. Res. Rep., 19, 10 Nakamura Y.; 1989: A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. ��������� ������ �� ������� ��������� �������� ���������� ������ Quarterly Report of Railway Technical Research Institute. Rept., 30 , pp. 25–33 Nogoshi M., Igarashi T.; 1970: On the propagation charactestics of the microtremors . Journal of the Seismological Society of Japan, 24 , pp. 24-40.