GNGTS 2015 - Atti del 34° Convegno Nazionale

Priolo E., Barnaba C., Bernardi P., Bernardis G., Bragato PL, Bressan G., Candido M., Cazzador E., Di Bartolomeo P., Durì G., Gentili S., Govoni A., Klinc P., Kravanja S., Laurenzano G., Lovisa L., Marotta P., Ponton F., Restivo A., Romanelli M., Snidarcig A., Urban S., Vuan A., and Zuliani D.; 2005. Seismic monitoring in north-eastern Italy: A ten-year experience. Seismological Research Letters , 76, 446–454 Priolo, E., Laurenzano, G., Barnaba, C., Bernardi, P., Moratto L., and A. Spinelli; 2015a. OASIS: The OGS Archive System of Instrumental Seismology. Seismological Research Letters 05/2015; 86(3):978-984. DOI:10.1785/0220140175 Priolo E., M. Romanelli, M. P. Plasencia Linares, M. Garbin, L. Peruzza, M. A. Romano, P. Marotta, P. Bernardi, L. Moratto, D. Zuliani, and P. Fabris; 2015b. Seismic monitoring of an underground natural gas storage facility: the Collalto Seismic Network. Seismological Research Letters , 86 (1), 109-123 + esupp, doi: 10.1785/0220140087. SITE CLASSIFICATION SCHEME FOR A COMPLEX GEOLOGIC AREA: THE STUDY CASE OF MT. ETNA F. Panzera 1 , E. Longo 2,3 , H. Langer 2 , G. Lombardo 1 , S. Branca 2 1 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università degli Studi di Catania, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Etneo, Catania, Italy 3 Department of Geosciences, University of Malta Introduction. The features of near surface geology as well as the morphologic setting and the water content of layers play a key role in controlling ground motion. The most common technique of site response estimation is the standard spectral ratio (SSR) that consists in comparing earthquake recordings at two sites, the first of which is located on soft sediments (target site) and the other on hard rock (reference site) (Borcherdt, 1970). The method provides reliable evaluations if the “reference site” is free from any site effect, as for instance if it is located on an un-weathered, horizontal bedrock. Another extensively used technique, that does not need a reference station, consists in the spectral ratio between the horizontal and the vertical components of the shear wave part of the earthquake recordings (HVSR). This method, first applied by Lermo and Chavez-Garcia (1993) and subsequently by Lachet et al. (1996), exhibits very encouraging similarities with the SSR technique, especially in frequency values of resonant peaks, when the S-waves are used (see Riepl et al., 1998; Parolai et al., 2001 and references therein). According to the above mentioned studies HVSR is well correlated with surface geology, and much less sensitive to source and path effects. However, peak amplitudes depend on the type of incident waves; consequently, the determination of the absolute level of amplification only through HVSR is not straightforward (Field and Jacob, 1995). A quick estimate of the site effects role in the seismic motion observed at the surface can be provided by the horizontal to vertical noise spectral ratio technique (HVNR). Although ���� ������� many authors (e.g., Mucciarelli, 1998; Rodriguez and Midorikawa, 2002) have questioned the existence of simple direct correlation between HVNR spectral amplitude values and the site amplification, t��� ������� ��� ���� �������� �� �������� ������� ������ ������ ���� �� ������ ����� ����� his method, put into practice by Nakamura (1989), became widely used in recent years since it provides a reliable estimate of the fundamental frequency of soft soil deposits (Lermo and Chavez-Garcia, 1993; Seekins et al., 1996). The HVNR from ambient vibrations are sometimes “non-informative”, particularly in the case of significant lateral heterogeneity giving rise to 2D/3D effects and velocity inversion that influence the vertical component of motion (Di Giacomo et al. , 2005; Panzera et al., 2013). The selection of specific elastic response spectra according to “soil categories” is the easiest way to account for site effects in engineering projects and general-purpose hazard maps. Most of the international seismic codes make use of the average shear wave velocity of the upper 30 m (V S,30 ) to discriminate soil categories (Eurocode, NEHRP). Some doubts arise about the 142 GNGTS 2015 S essione 2.2