GNGTS 2013 - Atti del 32° Convegno Nazionale

group (of about 80 stations) that amplify about half of a generic site classified as ‘A’ in the EC8 code. On the other hand there are some groups, namely ‘L2’, ‘B2’ and ‘H2’, for which the amplification are much higher than those obtained for the EC8 class by the ground motion prediction equation developed in Bindi et al. (2011), respectively in the low, medium and high frequency range. Identification of proxies for site classification. Considering the criteria explained in the previous section, we analysed 230 recording stations (of the about 800 available) but only 30 of them have a detailed geophysical and geotechnical characterization (V S profile, horizontal to vertical spectral ratio of ambient noise recordings, HVSR, and horizontal to vertical response spectra ratio, HVRS); about 60 stations have HVSR and HVRS, while the majority, about 110 cases, are only characterised by HVRS. With the available information, we were not able to derive a sufficient number of proxies for each class (Tab. 1). The considered proxies are: V S,30 , fundamental frequency of the site f 0 , shape of the HVSR curve and standard stratigraphic column (Fig. 3). Tab. 1 – Proxies for identification of the soil classes. CLASS V S,30 [m/s] V S,30 std [m/s] # of V S,30 f 0 noise [Hz] f 0 noise std [Hz] # of noise measurements predominant HVSR types stratigraphic column F 696 186 6 4.7 1.6 7 F, HF 1 B1 577 148 12 3.1 1.6 7 MF 2, 3 B2 440 52 3 ― ― 1 ― 2, 3 L1 296 98 7 0.7 0.07 3 LF 3, 4 L2 182 74 6 0.5 0.32 6 LF 3, 4 H1 656 186 4 5.0 ― 2 ― 1, 2 H2 454 114 2 ― ― 1 ― 1, 2 Fig. 3 – Standard stratigraphic columns. 316 GNGTS 2013 S essione 2.2