Non uniqueness in surface wave inversion and consequences on seismic site responce analysis

Surface wave tests are based on the solution of an inverse problem for shear wave velocity profile identification from the experimentally measured dispersion curve. The main criticisms for these testing methodologies are related to the inverse problem solution and arise from the possible equivalence of different shear wave velocity profiles in terms of their dispersion curve response: several set of model parameters can give very similar results that equally fit the experimental data. In this paper some implications of solution non-uniqueness towards the use of surface wave tests for seismic response studies are investigated using both numerical simulations and experimental data. A Monte Carlo approach for the inversion problem has been used to obtain a set of equivalent shear wave velocity models by means of a statistical test which takes into account both data uncertainty and model parameterization. This set of solutions (i.e. soil profiles) is then used to evaluate the seismic response with a conventional one-dimensional analysis. It is shown that equivalent profiles with respect to surface wave testing are equivalent also with respect to site amplification thus reducing the criticism related to inversion uncertainty for the engineering use of surface wave tests.