GNGTS 2015 - Atti del 34° Convegno Nazionale

aptitude of V S,30 to predict actual soil amplification in Etna volcano as well as in different part of the world. Recent studies pointed out that the main problems are: alternating outcrops of sediment and lava (Panzera et al. , 2011), oriented fractures linked to the fault fabric (Rigano et al. , 2008; Di Giulio et al. , 2009; Panzera et al. , 2014, 2015), velocity inversion (Panzera et al. , 2015). Then, a possible solution is to adopt a “Predominant-Period Site Classification”. In the present study we test the reliability of using both ambient noise and earthquake recordings in the lower eastern flank of Mt. Etna, a rather complex geologic and topographic setting, characterized by velocity inversion as well as strong vertical and lateral heterogeneities. The seismic site response of the study area was investigated by adopting the most commonly used techniques to evaluate the site response properties, such as the HVSR and the HVNR. Moreover, a detailed analysis of the geologic setting to reconstruct the stratigraphic sequence of 19 seismic stations of the INGV - Osservatorio Etneo was performed (see location in Fig. 1). These data with a velocity model built through literature information were used to achieve 1D amplification function for the Etnean area. Earthquake and ambient noise spectral ratios. The HVSRs were performed selecting local earthquake records, extracted from the INGV - Osservatorio Etneo database, whose location and magnitude were taken from the corresponding bulletins. The data set includes 30 earthquakes with local magnitude greater than 2.5, which occurred in the entire volcanic area. Recorded earthquakes were base-line corrected, with the purpose of removing spurious offsets and band-pass filtered in the range 0.08-20 Hz, with a fourth order causal Butterworth filter. The analysis was performed by using 20s time windows, starting from the S-wave onset, including part of the coda and using a 5% cosine-tapered window. First of all, Fourier spectra, Fig. 1 – Mean HVSR (black line) and mean HVNR (red line) at each considered seismic station with the corresponding standard deviation, dashed black and red respectively. GNGTS 2015 S essione 2.2 143