GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 In partcular, the following parameters varied across sites: i) number of sensors, ranging from 11 to 46; ii) acquisiton layout; iii) maximum array aperture, ranging from 100 to 200 m; iv) recording duratons, ranging from 1.5 to 15 hours. Single staton data have been analysed by Horizontal-to-vertcal spectral rato method (H/V), considering also its azimuthal amplitude variaton, while Rayleigh wave 3-component beamforming method (RTBF) has been adopted for array data processing. Preliminary results obtained at seismic monitoring sites showed spatally consistent results across each array in terms of H/V functons, but only in the low frequency range, where low resonance frequency peaks (f_0<2 Hz) were ofen observed. Such resonance peaks displayed large amplitude variatons, up to 50 %, as a functon of the considered horizontal directon (Fig. 2). In the high frequency range (f>2 Hz), individual H/V functons across each array showed large diferences in terms of amplitudes and secondary resonance frequencies (f_1), which suggests a large variability in the shallow elastc propertes distributon within a short area. In few cases, H/V functons calculated across actve tectonic structures showed signifcant variatons in terms of amplitude and shape, which are interpreted as correlated to the shallow sedimentary structure of the subsurface caused by such faults. RTBF analysis performed on data acquired at seismic monitoring sites, showed clear dispersion curve (DC) images both for Rayleigh and Love wave, within a variable frequency range (2-10 Hz). While Love DC data appear dominated by the fundamental mode, Rayleigh-wave dispersion images showed a signifcant contributon of higher modes (Fig. 3), which support the idea of a complex subsurface model characterised by inverse dispersive propertes with depth. Such preliminary fndings suggest a rather complex subsurface structure at the investgated sites on Etna volcano, whose reconstructon should be supported by advanced array processing and carefully considering all available geological informaton.