Time-weighted average shear wave velocity profiles from surface wave tests through a wavelength-depth transformation

We investigate the possibility of obtaining time-weighted average shear wave velocity profiles through a wavelength-depth transformation of experimental dispersion curves from surface wave tests, without a formal solution of the inverse problem. We evaluate this approach on a wide flat-file database (Polito Surface Wave Database, PSWD) of experimental dispersion curves and related shear wave velocity profiles, both from dispersion curve inversion and invasive tests. The results show that the proposed wavelength-depth transformation can be valuable for seismic site evaluations offering an estimation of time-weighted average shear wave velocity profiles very similar to a state-of-the-art inversion of the experimental dispersion curves and with similar uncertainty with respect to invasive tests. This transformation has the advantage of avoiding time-consuming inversion processes, with related uncertainty sources, and any assumption on layer parameterization and a-priori information. Moreover, in conjunction with an experimental evaluation of the fundamental frequency of the site, from independent surveys, the wavelength-depth transformation can be used to get a direct and fast estimate of the position of the engineering bedrock.