GNGTS 2019 - Atti del 38° Convegno Nazionale

672 GNGTS 2019 S essione 3.2 phenomenon. To make clearer the presence of inversion, the standard spectral ratio (SSR) was calculated between the vertical components of the measurements carried out in surface with respect to the vertical component of a reference site related to a sampling performed on the lava tube floor (Fig. 2c, d, e) (Sgarlato et al. , 2011). The graphs (Fig. 2c, d) highlight a strong and clear amplification peak of the vertical component around 9-10 Hz, up to 15 times to the vertical component of reference site. Fig. 2 - H/V spectra, related to the acquisition performed along the A-A’ (a) and B-B’ (b) profile (see figure 1c for location); b) photo of HVSR survey inside the cave; graphs obtained by Standard Spectral Ratio (SSR) between the vertical components of the measurements carried out along A-A’ (d) and B-B’ (e) alignments with respect to the vertical component of a reference site, related to a sampling performed on the lava tube floor. Through directional analysis, more pronounced amplification effects have been highlighted in a parallel direction to lava tube elongation, such effects result characterized by a specific directionality of the ambient seismic noise, in the N 30°-40° azimuth direction. This could “imply” the of shear waves polarization in a direction parallel to the lava tube elongation. Integrating the results obtained from the HVSR surveys with the information, on the shear waves velocity distribution with the depth, obtained by the MASW-HVSR joint fit procedure,