GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 675 linearity of the particle motion and polarization in a direction perpendicular to the strike of the main joints identified in the rock mass; these peaks are probably related to the vibrational behaviour of the rock blocks composing this portion of the rock slab edge. The analysis of the SNS data allowed to detect several near-field weak earthquakes whose analysis confirmed the presence of a H/V peak in the former camping area related to a 1-D resonance. At the same time, several local microseismic events were detected and characterised by the Nanoseismic Monitoring software. Some of these events presents a pretty-regular waveform and are originated at shallow depth in centre of the historic village, therefore they are probably produced by anthropic activities. On the contrary, other microseismic events seem to have a natural origin because their waveform is not regular. Moreover, hypocentres are located at depth in the North-East portion of the slab, where open fractures cross the rock mass. These events are probably related to the evolution of the gravity-driven instability process that involves the slab edge. Conclusions. The seismic ambient noise measurements performed at San Leo allowed to point out the following relevant features of the local seismic response: i) presence of a 4.5 Hz frequency resonance related to anthropic activities; ii) absence of resonances in the historic village, except for 1-D resonance in the parking lot and the former camping area; iii) polarization of the particle motion in the rock slab edge area, upslope the detachment areas of the 2014 landslide, probably related to the presence of fractures and unstable rock blocks. At the same time, the analyses carried out on the SNS array continuous data allowed to detect and characterise several microseismic events originated in the rock slab edge area, that confirm ongoing slope instability processes. References Borgatti L., Guerra C., Nesci O., Romeo R.W., Veneri F., Landuzzi A., Benedetti G., Marchi G. and Lucente C.C.; 2015: The 27 February 2014 San Leo landslide (northern Italy) . Landslides, 12(2) , 387-394. Bour M., Fouissac D., Dominique P. and Martin C.; 1998: On the use of microtremor recordings in seismic microzonation . Soil Dyn. Earthq. Eng., 17(7-8) , 465-474. Burjánek J., Moore J.R., Yugsi Molina F.X. and Fäh D.; 2012: Instrumental evidence of normal mode rock slope vibration . Geophys. J. Int., 188(2) , 559-569. Field E.H. and Jacob K.H.; 1995: A comparison and test of various site-response estimation techniques, including three that are not reference-site dependent . Bull. Seism. Soc. Am., 85 , 1127-1143. Fiorucci M., Iannucci R., Lenti L., Martino S., Paciello A., Prestininzi A. and Rivellino S.; 2017: Nanoseismic monitoring of gravity-induced slope instabilities for the risk management of an aqueduct infrastructure in Central Apennines (Italy) . Nat. Hazards, 86(S2) , 345-362. Galea P., D’Amico S. and Farrugia D.; 2014: Dynamic characteristics of an active coastal spreading area using ambient noise measurements-Anchor Bay, Malta . Geophys. J. Int., 199 , 1166-1175. Haghshenas E., Bard P.-Y., Theodulidis N. and SESAME WP04 Team; 2008: Empirical evaluation of microtremor H/V spectral ratio . Bull Earthq. Eng., 6 , 75-108. Iannucci R., Martino S., Paciello A., D’Amico S. and Galea P.; 2018: Engineering geological zonation of a complex landslide system through seismic ambient noise measurements at the Selmun Promontory (Malta) . Geophys. J. Int., 213(2) , 1146-1161. Joswig M.; 2008: Nanoseismic monitoring fills the gap between microseismic networks and passive seismic . First Break, 26 , 121-128. Lermo J. and Chavez-Garcia F.; 1993: Site effect evaluation using spectral ratio with only one station . Bull. Seism. Soc. Am., 83(5) , 1574-1594. Nakamura Y.; 1989: A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface . Quarterly Report of Railway Technical Research Institute (RTRI), 30(1) , 25-33.