GNGTS 2022 - Atti del 40° Convegno Nazionale

492 GNGTS 2022 Sessione 3.3 through the interpretation of the dispersion curves but through the multi-component Full- Velocity Spectrum (FVS) approach (Dal Moro et al. , 2015a; 2015b; 2019; Dal Moro, 2019; 2020). The result (V S profile shown in Fig. 3e) is apparently very similar to the one obtained by considering the joint analysis of the phase velocities of the Z and T components together with the HVSR (see Fig. 1). Conclusions. Accomplished analyses allow to highlight the following evidences: 1) Rayleigh-wave modelling cannot be performed considering an approach based on the modal dispersion curves and the use of the effective curves (for passive data) or the FVS (for active data) is crucial; 2) Because of the intrinsic (i.e. inevitable) ambiguity of the dispersion curve, Rayleigh- wave modelling based on the effective curve does not ensure the correctness of the obtained V S profile even when performed jointly with the HVSR; 3) Especially when analysing phase velocities, the acquisition and analysis of Love waves reveal decisive to constrain an inversion procedure capable of providing a robust solution free from significant ambiguities; 4) Love-wave dispersion can be effectively obtained from passive data via ESAC even while considering linear arrays (data and analyses are not affected by significant directivity issues); 5) The holistic analysis of multi-component group velocities and RPM curves based on the FVS approach reveal an effective way to obtain robust shear-wave profiles. Since a solution needs to be of general validity, it is therefore clear that phase velocity analyses based just on Rayleigh waves are not recommended because, due to the complex contribution of different modes, they can lead to overestimated Vs values even if the analyses are accomplished jointly with the HVSR. Due to their simpler phenomenology, Love waves represent an essential tool to properly constrain an inversion procedure. On the other side, the holistic analysis of multi-component group velocities and RPM data appear an extremely efficient alternative both because it requires a simpler acquisition setting, both because, thanks to the possibility to deal with a large number of observables, it leads to a V S profile free from major ambiguities. References Arai H. and Tokimatsu K.; 2005: S-wave velocity profiling by joint inversion of microtremor dispersion curve and horizontal-to-vertical (H/V) spectrum . Bull. Seismol. Soc. Am., 95 , 1766-1778. Arai H. and Tokimatsu K.; 2004: S-wave velocity profiling by inversion of microtremor H/V spectrum . Bull. Seismol. Soc. Am., 94 , 53–63. Cho I., Tada T. and Shinozaki Y.; 2006a: Newmethods of microtremor exploration: the centreless circular array method and two-radius method . In: Proceedings of the third international symposium on the effects of surface geology on seismic motion, Grenoble (France), 30 Aug-1 Sept, pp 335–344. Cho I., Tada T. and Shinozaki Y.; 2006b: Centerless circular array method: inferring phase velocities of Rayleigh waves in broad wavelength ranges using microtremor records . J. Gophys. Res., 111 , B09315. Cho I., Senna S. and Fujiwara H.; 2013: Miniature array analysis of microtremors . Geophysics, 78 : KS13–KS23. Dal Moro G.; 2020: Efficient Joint Analysis of Surface Waves and Introduction to Vibration Analysis: Beyond the Clichés , Springer, ISBN 978-3-030-46303-8, 273 pages Dal Moro G., Al-Arifi N. and Moustafa S.R.; 2019: On the efficient acquisition and holistic analysis of Rayleigh waves: Technical aspects and two comparative case studies , Soil Dynamics and Earthquake Engineering, 125 , 105742, https://doi.org/10.1016/j.soildyn.2019.105742 Dal Moro G.; 2019: Surface wave analysis: improving the accuracy of the shear-wave velocity profile through the efficient joint acquisition and Full Velocity Spectrum (FVS) analysis of Rayleigh and Love waves . Exploration Geophysics, 50 , 408-419, DOI: 10.1080/08123985.2019.1606202