GNGTS 2013 - Atti del 32° Convegno Nazionale

Fig. 1 compares results from 1D numerical simulation with horizontal-to-vertical (H/V) spectral ratios calculated using waveforms recorded by temporary (mostly velocity meters) and permanent (accelerometer) seismic stations. The NTC08 amplification levels provided for category B and category C ground profiles are also shown. While at Mirandola and Casaglia, the dominant period ranges highlighted by 1D amplification curves agree with those indicated by H/V ratios, they are not consistent with the experimental H/V curve at Soncino (ORZI station, about 4 km away), which does not suggest any particular amplification peak. This suggests that ORZI station, though quite near to Soncino and within the same ground type class, has a different soil amplification behavior. Similar considerations hold by comparing the NTC08 amplification functions with those obtained from 1D numerical simulation. The NTC08 spectral amplification factors appear adequate for a site like Casaglia and nearly adequate at a very deep soil site like Mirandola, but they are not adequate for a site like Soncino, where significant soil amplification is found only below 0.1s Ground shaking hazard (GSH) results. As specified in the foreword, GSH calculations were performed at different scales. As an example, Fig. 2b shows the GSH map for PGA de- termined by applying the NTC08 soil factors (which were assigned to each node of the calculation grid on the grounds of the soil zonation map shown in Fig. 2a) to the ref- erence rock ground motion haz- ard maps developed by the MPS Working Group (2004) for a mean return period (MRP) of 475 years. GSH maps were also produced for other spectral periods and by applying site factors proposed by other building codes, such as those suggested by Eurocode 8 (Com- itè Europèen de Normalisation – CEN, 2004). The salient results are sum- marized in Fig. 3 where the GSH estimates obtained from the appli- cation of the different approach- es used here are compared and contrasted, in terms of Uniform Hazard 5%-damped acceleration response spectra. Before going to the final comments, it should be noted that Level 1-to-3 spectra should not be directly compared with those labelled as “Level 4” because the rock spectra used as a point of departure were derived Fig. 2 – Map of ground type zonation for Northeastern Italy (a) and GSH map for Northeastern Italy, representing the PGA values with a 475-year mean return period (b). 19 GNGTS 2013 S essione 2.1