GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 381 Moving from the old classification to the new one (Tab. 3), most of the stations (91%) does not change soil category. Number of A sites decreases (-46%), while B and E sites increase (+15% and +50%); the numbers of C and D are about similar. Residual analysis. For performing the residual analysis, it is necessary to employ one or more Ground Motion Models (GMMs) predicting the values of intensity measures (IMs). For this purpose, we selected 3 GMMs: ITA10 (Bindi et al. , 2011), valid for the Italian territory, BND14 (Bindi et al. , 2014), calibrated using pan-European strong motion data, and the global model CZ15 (Cauzzi et al. , 2015). In addition, we also considered the combination of the three GMMs (MIX model) according to the logical tree of ground motion used for the new model of Italian Seismic Hazard Map, by assigning the same weight coefficients ( w ITA 10 = 0.45, w BND 14 = 0.32, w CZ 15 = 0.23). The analysis consisted in calculating the total residuals as logarithm difference between IMs observations on site and predictions of GMMs. Therefore, the total residuals were decomposed by means the random effects model (Stafford, 2014), in order to extract the systematic term for each station, δS 2 S S . This term quantifies the average misfit of recordings from one particular site with respect to the event-corrected median ground motion (Lanzano et al. , 2017). If this term is calculated with respect to the reference level of the GMM, (i.e. the EC8-A class for ITA10 and BND14 and V S ,30 = 800 m/s for CZ15), it can be considered as a proxy of the site amplification ( δS 2 S A ). Owing the predominantly low and moderate level of recorded motions in our analysis, the δS 2 S A are computed assuming linear soil behavior. Table 3 - Correlation matrix between NTC08 and NTC18 of 138 accelerometric stations in ESM flatfile. NTC18 → NTC08 ↓ A B C D E A 34 26 0 0 3 B 0 161 0 0 2 C 0 0 123 0 1 D 0 0 0 8 0 E 0 0 0 0 12 Fig. 2 - δS 2 S A trend for station CLF according to ITA10, BND14, CZ15 and MIX.