GNGTS 2014 - Atti del 33° Convegno Nazionale

More pronounced and dominant spectral ratio peaks were observed in tall and isolated buildings whereas, secondary spectral ratio peaks were observed in case of adjacent buildings, independently from their typology of construction (see examples in Fig. 3). It is interesting to mention that the fundamental periods experimentally evaluated appear smaller than those obtained through the use of the relationships proposed by the official norms ������ ����� (OPCM, 2005; Eurocode8, 2003)�. We can finally affirm that the use of ambient noise records showed to be a reliable and not expensive technique for a quick characterization of the local seismic response and the experimental evaluation of building fundamental periods, as well as investigations about possible soil-to-structure interactions. This kind of studies appear to be particularly useful to governmental agencies tasked with emergency response and rescue. Indeed, ���������� performing a detailed geologic study, together with the evaluation of the local seismic response and the dynamical properties of buildings in the island of Lampedusa has given significant suggestions about potential critical conditions due to soil-structure interaction and local amplification phenomena. The results obtained can be summarized as follow: - A detailed survey, especially performed in the areas of major interest from the geological point of view, such as landslide prone areas was carried out; - In the Cala Creta Fault area a careful geological descriptions and stratigraphic logs were provided; - The integration of Grasso and Pedley (1985) findings with new stratigraphic and structural analyses, allowed obtaining a more precise attribution of the different litho-stratigraphic units. - The complexity of the near-surface geology, as well as the morphology strongly influence the local amplification of the ground motion and the occurrence of directional effects. - ����� ������������� ������� ���� ����� �� ��� ���� �������� ���� ��������� ���� �� ��� Major amplification effects take place on the soft deposits that partially fill up the incisions of old pre-existing streams and mostly in the neighbouring of both morphologic escarpments and faults. On the contrary, HVNR with not significant spectral ratio peaks are observed on the calcareous plateau. - Rotated spectral ratios and polarization analysis highlight the presence of evident directional effects in proximity of both faults and cliffs. The polarization of the wave-field assumes major values at wide angles (between 60°-90°) with respect to the structures strike. - Spectral ratios of the ambient noise measurements provided reliable estimates of the fundamental period of analyzed buildings. The measured periods were used to obtain period-height relationships which set into evidence that the experimental values are lower than those postulated by Eurocode8 (2003). Such finding could be explained by considering the contribution of the infill walls that modern codes do not consider adequately. - Significant differences were observed between the fundamental periods obtained for reinforced concrete and masonry buildings, the former being usually higher than the latter. This behaviour appear related to the different stiffness of the structures and to the presence of connected adjacent buildings. Acknowledgements. The present study is financially supported by the Italo-Maltese research project SIMIT (Costituzione di un Sistema Integrato di Protezione Civile Transfrontaliero Italo-Maltese). References Argnani A.; 1990: The Strait of Sicily rift zone: foreland deformation related to the evolution of a back-arc basin . J. Geodyn. 12 , 311–331. Burjánek J., Gassner-Stamm G., Poggi V., Moore J. R. and Fäh D.; 2010: Ambient vibration analysis of an unstable mountain slope , Geophys. J. Int., 180 , 559-569, doi: 10.1111/j.1365-246X.2009.04451.x. Burjànek J., Moore J.R., Molina F.X.Y. and F�� ��� ����� äh ��� ����� D.; 2012: Instrumental evidence of normal mode rock slope vibration . Geophys. J. Int., 188 , 559-569. Civile D., Lodolo E., Tortorici L., Lanzafame G. and Brancolini G.; ����� 2008: Relationships between magmatism and tectonics in a continental rift: the Pantelleria Island region (Sicily Channel, Italy) . ������ ������� Marine Geology 251 , 32-46. 208 GNGTS 2014 S essione 2.2