GNGTS 2022 - Atti del 40° Convegno Nazionale

262 GNGTS 2022 Sessione 2.2 reduce the variability of the fitting models. In the work of Del Gaudio et al. (2021), we used in combination electrical resistivity tomography (ERT), to extract from resistivity profiles, the thickness of the most superficial layer. The velocity vertical profiles resulted from the inversion of ellipticity curves at each ambient noise measurement station of a profile are synthesized in a Vs cross section (Fig. 2a). Fig. 2 - a) Cross section which synthesizes velocity ground profiles resulted from the inversion of the ellipticity curves. The dashed line represents the streambed profile (from Del Gaudio et al. , 2021); b) New cross section obtained from the joint inversion of the Rayleigh wave ellipticity curves and localized group velocity dispersion curves. During the noise data acquisition, following the recommendations proposed for the HVIP technique (Del Gaudio, 2017), a fix “reference station” was kept in continuous recording. Thus, in this work, we exploit the availability of simultaneous and synchronized noise recordings to test the possibility of reducing the ambiguity of data interpretation by integrating the modelling procedure with the outcome of another passive seismic technique based on the cross-correlation analysis of noise recordings (Bensen et al., 2007). This method can provide additional constraints for the subsoil velocity modelling from the calculation of dispersion curves of Rayleigh wave group velocities along the path between different couples of stations. Method. The method HVIP (Del Gaudio 2017), introduced to obtain more stable amplitude values of H/V than HVNR, consists of an instantaneous polarization analysis of ambient noise recording. The innovation of themethod consists in calculating themean H/V values only on the samples with Rayleigh wave polarization. The H/V ratio is calculated instant by instant, in the time domain, on temporal series filtered on narrow frequency bands, by means of an analytic transform. Extracting only wave packets with a clear Rayleigh wave polarization reduces the H/V variability deriving from changes of composition of the wavefield, whose components (P, S, Rayleigh and Love waves) differently contributes to the horizontal and vertical amplitude of ground motion. The cross-correlation method, applied to two simultaneous noise recording, in the hypothesis of a diffuse wave field, provides information about properties of the medium