GNGTS 2013 - Atti del 32° Convegno Nazionale

from different ground motion prediction equations (GMPEs). Rock spectra of Level 1-to-3 are based on the application of the Bindi et al. (2011) GMPE (hereinafter ITA10) modified with expressly calculated correction factors for ground-type A. These factors, which were properly estimated to correct the ground motion overestimation of the observed spectral ordinates by ITA10, are responsible for most of the differences in the results. In partial agreement with the current national hazard maps and hazard map disaggregation (Barani et al. , 2009), the Level 4 UH spectra were derived using the Ambraseys et al. (1996) GMPE, indicated as AMB96 in Fig. 3. The difference between the two approaches can be appreciated by comparing the rock UHSs in Fig. 3 (grey curves). It is evident that the corrected ITA10 GMPE produces hazard values that are 1.4 to 2.8 lower than those obtained by the attenuation relation of Ambraseys et al. (1996). This is obviously reflected in the GSH estimates on soil which are discussed below considering an MRP of 475 year: 1. Among the simplified approaches (Level 0-2), that labelled as “Level 0”, which – unlike those of Level 1 and 2 – does not make use of the rock-correction factors just mentioned, led to the highest spectral ordinates. At Mirandola, the Level 0 UHS does not differ significantly from that obtained from the Level 4 assessment (larger differences can be observed only in the spectral range 0.2.-0.7 s) Fig. 3 – Comparison of the UHSs corresponding to a MRP of 475 years obtained by applying the different approaches in Tab. 0.1: a) Mirandola, b) Casaglia, c) Soncino. 20 GNGTS 2013 S essione 2.1