GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 349 Fig. 3 - Comparison at ROM9 site between the shear-wave velocity profile (left) and the lithostratigraphical model (right). assigned computing the mean value of the shear-wave best velocity models in the uppermost 30 m (as prescribed by the national seismic design code). As example, Fig. 3 displays the comparison at ROM9 between the local Vs profile derived from surface-wave analysis and the lithostratigraphical log obtained from the geological analysis. The Vs profile of ROM9 is able to individuate the contact at a depth of about 50 m between the volcanic deposits and the underlying clay (Monte Vaticano Unit, Pliocene). In detail from top to bottom in the velocity model of Fig. 3: after few meters of very soft soil (Vs < 200 m/s), the volcanic deposits show Vs values of 400-500 m/s, whereas the consolidated clay of the Monte Vaticano Formation shows Vs values larger than 600 m/s. The Vs30 at ROM9 resulting from this model is 410 m/s, being B the corresponding soil class category following the national code. As general comment resulting from this experience, a correct use of the surface-wave methods integrated with geological data is able to provide a reliable Vs profile that can be used to include the local effects in the seismic response of the site. However, it is important to highlight that we do not obtain always a perfect match between dispersion curves derived at a same site when we used different array geometry and source. The reasons of these discrepancies are not clear and need deeper investigation. A final consideration is that a suitable site classification is possible only with accurate geological and geophysical surveys. In presence of a reliable estimation of the local velocity profiles at the sites where seismic stations are installed, strong-motion data can be properly used for seismic hazard and site response studies. References Foti et al. ; 2017: Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project, Bull Earthquake Eng, doi: 10.1007/s10518-017-0206-7. Pacor, F., Paolucci R., Luzi L., Sabetta F., Spinelli A., Gorini A., Nicoletti M., Marcucci S., Filippi L. and Dolce M.; 2011: Overview of the Italian strong motion database ITACA 1.0, Bull Earthquake Eng, 9(6), 1723–1739, doi: 10.1007/s10518-011-9327-6.