GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 All the above equipment was deployed in 2D confguraton, following nearly circular geometry, depending on the local logistc. Fig. 1 show an example of installaton, at the Casaglia site. The Le3D and Terrabot velocimeters were arranged in the feld with a maximum aperture varying from about 200 to 300 m (depending on site). The vertcal geophones, which are constrained by cables, were deployed in a circular ring of 50 m of aperture. All the data were processed with similar parameters, using the Geopsy tool (Wathelet et al . 2020). The comparison of the H/V curves (Fig. 2) shows that Le3D and Terrabot provide the same H/V spectral ratos, at the three selected sites, even if the f0 is well below the Terrabot eigen-frequency of 4.5 Hz. At the Casaglia site, the H/V curves show a consistent narrow and strong peak at 0.7 Hz, resultng from both Le3D and Terrabot instruments. The good agreement between Le3D and Terrabot is also verifed at the Ferrara site, where the f0 is at about 0.2 Hz. A good ft is also observed for the last site at Pieve di Cento, where the H/V curves do not show a clear peak, but rather a bump between 0.2 and 0.3 Hz (Fig. 2). Concerning the dispersion curves, we also observed a good ft between the three equipment typologies, taking into account the diferent geometry and number of receivers giving dispersion curves in diferent frequency bands. However, the resultng dispersion curves from Le3D, Terrabot and geophones show a good match in the nearly overlapping frequency band. For the Casaglia site, corresponding to a structural high zone of the Po Plain (Tarabusi and Caputo, 2017), we also present a joint inversion of the dispersion and H/V curves (Fig. 3). The Vs profle shows a main interface at about 140 m deep, corresponding to the angular unconformity, erosive top of the marine Miocene marls. The overlying Quaternary succession largely consists of alluvial plain deposits, showing a downward Vs increase from 120 to 450 m/s.