GNGTS 2015 - Atti del 34° Convegno Nazionale

For the S waves, the determined geometry is in agreement with the P waves obtained profile, even though with the limited length of the profile and the relative small number (18) of geophones used it is possible to image only two layers (Fig. 3). The S waves profile allows recognizing a surface layer characterized by a low velocity (about 150 m/s) and a small thickness (1-1.5 m), interpreted as the weathering. Conclusions. The passive and active seismic investigations made at four sites in Friuli Venezia Giulia allow the determination of the seismic characteristics of these sites. The presence of a reference site, as GEMO in our case where the borehole stratigraphy was available, represents an important starting point for the integrated approach affordability. In fact, it allowed to verify the results obtained with the different techniques by a direct calibration. The depth of the discontinuity found with F-K array based method is in agreement with the borehole information, confirming the validity of the obtained results. The resonant frequency found with the H/V spectral ratio of seismic noise was used, according to Haskell low, in combination with the bedrock depth to determine the average shear wave velocity of the sediments. In GESC site, H/V spectral ratio and F-K methods allowed to identify the presence of a discontinuity at the same depth. Furthermore, these results are in agreement with a gravimetric survey made in Gemona del Friuli (Furlanetto, 2004). The seismic refraction allowed the definition of a 2D velocity profile, down to a depth of about 15 m for P waves and about 10 m for S waves. The geometry of P and S profiles are similar, even if on the S profile it was also possible to recognize Fig. 3 – On the top, the geometry of the P waves seismic profile and the resulting velocity profile. On the bottom, the resulting S waves velocity profile. The velocity values are represented in a color scale; note that the colors scale for P and S waves is different. 188 GNGTS 2015 S essione 2.2