GNGTS 2015 - Atti del 34° Convegno Nazionale

Fig. 3 – Left panel: map showing the geographic distribution of recording stations presented in the next release of ITACA (ITACA 2.0). Right panel: distribution of site classification according to EC8 code for the stations with available shear-wave velocity profile (top) and distribution that include station categorized according surface geology (bottom). The recording stations are classified based on the Italian seismic provisions NTC08, which adopts a similar scheme as the EC8 Code. The seismic site response of the station is categorized according to the average shear – wave velocity between 0 and 30 m depth (V S,30 ), when available, or according to an expert judgment based either on surface geology or available geophysical information such as fundamental frequency. With respect the totality of recording stations included into ITACA database, only 1/6 is characterized with a measurement of the Vs profile. In particular, the database contains: 151 shear-wave velocity profiles for RAN station; 4 for the strong-motion network operated by ENEA (Agenzia nazionale per la nuove tecnologie, l’energia e lo sviluppo economic sostenibile), 6 for the University of Basilicata network, 5 for the Rete Sismica Nazionale operated by INGV, while the remaining 2 are for temporary network. Fig. 3 (right panel) shows the distributions of site classification according to EC8 code for the stations with available shear-wave velocity profile (top). Stations categorized according to surface geology (Di Capua et al. , 2011) are marked by an asterisk and are shown in the bottom of the right panel. These temporary categories can change, once the relative shear-wave velocity profiles are acquired. During the past INGV-DPC S2 Project, an extensive campaign of site characterization has been carried out, allowing to provide detailed site-specific characterization for about 50 recording sites. Notably, about 1/2 of the studied stations had changed their previously soil categories, assigned only on the basis of surface geology. As an example, the station MLD (Meldola) classified as A* in according to the surface geology, changed its soil category as C (V S,30 = 214 m/s) after the V S measurement. In general, the class affected by the largest error is class B*, as about half of the stations have been assigned to other classes after the experiments. This large uncertainty is probably due to 126 GNGTS 2015 S essione 2.2