GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 673 it was possible to plot in depth the H/V amplitude values that characterized the H/V spectra, thus reconstructing the impedance contrast sections (Grassi et al. , 2019; Imposa et al. 2016). The impedance contrast sections in Fig. 3a, b show a first impedance contrast at about 4-5 m of depth, this contrast is probably linked with the presence of soil and pyroclastic material on volcano rocks. Below this impedance contrast, between 7 and 12 m of depth, it is possible to observe an area characterized by HV amplitude values lower than 1. This area has characteristics that can be correlated with the position and geometry of the investigated lava tube. Considering the results obtained it seems reasonable to state that the integration of the geophysics methods used in this study can be considered suitable to the identification of underground cavities, as the “Snow Cave” lava tube. References Branca S., Coltelli M., Groppelli G. and Lentini F.; 2011: Geological map of Etna volcano, 1: 50.000 scale . Italian Journal of Geosciences, 130 (3), 265-291. doi.org/10.3301/IJG.2011.15   Castellaro S. and Mulargia F.; 2009: The effect of velocity inversions on H/V , Pure Appl. Geophys., 166(4), 567–592. DOI 10.1007/s00024-009-0474-5 Grassi S., Imposa S., Patti G., Boso D., Lombardo G. and Panzera F.; 2019: Geophysical surveys for the dynamic characterization of a cultural heritage building and its subsoil: The S. Michele Arcangelo Church (Acireale, eastern Sicily) . Journal of Cultural Heritage, 36, 72-84. DOI 10.1016/j.culher.2018.09.015 Ibs-von Seht M. and Wohlenberg J.; 1999: Microtremor measurements used to map thickness of soft sediments . Bulletin of the Seismological Society of America, 89(1), 250-259. Imposa S., Grassi S., De Guidi G., Battaglia F., Lanaia G., and Scudero S.; 2016: 3D subsoil model of the San Biagio ‘Salinelle’mud volcanoes (Belpasso, SICILY) derived from geophysical surveys . Surveys in Geophysics, 37(6), 1117-1138. DOI 10.1007/s10712-016-9380-4 Nakamura Y.; 1989: A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface . Railway Technical Research Institute, Quarterly Reports, 30(1). Sgarlato G., Lombardo G. and Rigano R.; 2011: Evaluation of seismic site response nearby underground cavities using earthquake and ambient noise recordings: A case study in Catania area, Italy . Engineering Geology, 122(3- 4), 281-291. DOI 10.1016/j.enggeo.2011.06.002 Fig. 3 - Impedance contrast sections obtained from seismic ambient noise samplings: A-A’ section (a) e B-B’ section (b), the red lines indicate the intersection between the two section (see Fig. 1c for location).