The geophysical exploration with the surface waves makes it possible to obtain, with simplicity and cheapness, the propagation velocity of the S waves in the subsoil.
The MASW (Multichannel Analysis of Surface Waves) method allows the determination of the Vs30 speed profile.
It overcomes some of the limitations present in the refraction technique such as speed reversal.
It does not require long times in the acquisition phase and good results even in the presence of noise.
Rayleigh waves, in a stratified medium, are dispersive by propagating with different phase velocities and group velocities. They are recorded along the layout of geophones artificially energizing and are subsequently analyzed through complex computational techniques based on a multi-layered terrain recognition approach. Observing the frequency spectrum it is possible to highlight that the S wave propagates at a variable speed according to its frequency, as a result of the dispersion phenomenon. Once the pick-up on the f-K spectrum or on the dispersion curve obtained from the campaign data was carried out, by means of inversion processes, the velocity profile is obtained with the depth that allows to define the parameter of Vs30.
Re.Mi. analysis (Refraction Microtremor) is a passive seismic technique that records microtremors, due to natural sources (wind, sea, anthropic activity), through multi-geophonic dispositions. Also with this methodology the dispersive properties of Rayleigh waves are studied.
During the analysis, the velocity spectra are determined for various time windows of the recording made of which one chooses the most clear for the identification of the curve to be inverted in a similar way to the MASW analysis, however, unlike the latter, it is a method chosen for surveys in particularly noisy areas and has a higher resolution in determining the deeper layers.