VS and VP vertical profiling via joint inversion of Rayleigh waves and refraction travel times by means of bi-objective evolutionary algorithm

Rayleigh wave dispersion curves and refraction travel times are jointly inverted through a procedure based on a Multi-Objective Evolutionary Algorithm (MOEA) technique. The proposed procedure aims at improving the reconstruction of subsurface structure by exploiting the complementary information attainable by refraction seismics and surface-wave dispersion and by overcoming in this way the problems related to non-uniqueness of the solution (surface waves and refraction seismics) and hidden layers (refraction).The proposed scheme allows the joint inversion of the data and the validation of the provisional interpretation. In fact, Pareto front symmetry proves to be a valuable tool to verify the coherency of the adopted interpretation as an incorrect number of layers, refractor attribution or assumed Poisson values reflect in non-symmetric Pareto front as well as in wider model distribution in the objective space.Methodology is initially tested using synthetic data and successfully applied to a field dataset resulting from a single standard seismic survey with vertical geophones and vertically-incident seismic source (sledgehammer).