GNGTS 2022 - Atti del 40° Convegno Nazionale

490 GNGTS 2022 Sessione 3.3 Fig. 1 - Purely passive data: shear-wave velocity profile ( c plot) obtained through the joint analysis of the phase- velocity effective dispersion curves of the Z ( a plot) and T ( b plot) components together with the HVSR curve ( d plot). In the a and b plots, the background colours represent the field data while the overlaying white curves are the effective dispersion curves of the identified subsurface model. In the d plot, the α value (0.2) in the legend represents the amount of Love waves in the microtremor field (Arai and Tokimatsu, 2004; Dal Moro, 2020). This is a very common problem (mistake) due to the intrinsic ambiguity of the Rayleigh- wave effective curve which, whether considering active or passive data, can be explained by a large variety of energy distribution and therefore models (Dal Moro, 2020) which cannot be solved by the HVSR (which, in turn, suffers from major non-uniqueness issues). In this case, Fig. 2 - Result of the joint analysis of the phase-velocity effective dispersion curve of the Z component ( a plot) and the HVSR ( b plot). The ambiguities of the Rayleigh-wave effective dispersion curve (and HVSR) are such that the obtained shear-wave velocities (V S profile shown in the c plot) overestimate the actual values. Compare with the result presented in Fig. 1 and see text for comments.