GNGTS 2014 - Atti del 33° Convegno Nazionale

differences in the local seismic response; as it resulted from this comparison the first resonance mode range between 0.5-4.5 Hz, with a maximum FFT-spectral of 5. The higher resonance modes are represented by a minimum of 3 up to 6 in a frequency range 3-15 Hz. Moreover, a geological-cross section passing from the “Europarco Business Park” was discretized by 56 soil columns, whose lateral representativeness is of about 10 m, in order to obtain the 1D spatial distribution of the A(f) under free field conditions and by assuming a linear model performed by the EERA code. The obtained A(f) distribution (Fig. 2a) is influenced by the stratigraphic effect only, i.e. related to the thickness of the alluvial deposits (including the recent alluvia and part the Paleo Tiber 4 deposits) with respect to the seismic bedrock depth. In particular, it is worth noticing that the first resonance mode range very closely between 0.5-0.6 Hz and remains constant for a large part of the cross section where the thickness vary in a range 35-65 m; on the contrary, in the portion of the valley where the thickness of the alluvia significantly decrease (15-20 m), due to the local structural setting, the first resonance mode corresponds to higher frequency values Fig. 2 – Results of the 1D numerical modeling of the 56 soil columns composing the geological cross-section FF’: a) contour map of the A(f) vs distance along the section b) geological cross-section FF’ Legend: Recent alluvial deposits (18 ky-present): lithological units from 1 to 7. Deposits of the volcanic district of Alban Hills and of the M. Sabatini (561-360 ky): lithological unit 8. PaleoTiber 4 deposits (Santa Cecilia Formation) 650-600 ky: lithological units from 9 to 12. Plio-Pleistocenic bedrock “Marne Vaticane - Monte Mario - Monte delle Piche Formation”: lithological units 13-14. GNGTS 2014 S essione 2.2 297