GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 671 Through the contouring of data related to seismic noise samplings performed, at regular interdistance, along each alignment, it was possible to obtain the impedance contrast sections. These sections show the distribution of HV amplitude value in the subsoil. Results and conclusions. All the H/V spectra related to the acquisitions performed at the surface show a similar trend (Fig. 2a, b). Are clearly detectable two main frequency peaks associable with as many impedance contrasts in the subsoil. The first, at lower frequency, around 1.1-1.3 Hz is related to a deeper impedance contrast; the second one included in 15-20 Hz frequency range, can be associated to a shallow impedance contrast probably linked to the transition between soil and pyroclastic material and underlying volcanic rock. The frequencies related to the depth range affected by the lava tube is included between these two spectral peaks in the frequency interval 6-12 Hz. In this frequency range, the spectra are affected by inversion Fig. 1 - a) Collocation of “Snow Cave”; b) geological map of Mt. Etna NE Flank area (extracted from the Geological Map of Etna Volcano 1:50000, Branca et al. , 2011); c) location of the ambient noise measurements (green) and relative profiles (red); A-A’ and B-B’ are the two section across the Cave; yellow symbol indicate the measurement used for the joint-fit; A-B=MASW section; Red circles= Geophones.