Cavity effect on Rayleigh wave dispersion and P-wave refraction

Sinkholes and cavities can represent serious hazards to human safety and urban infrastructures, cause roadbed subsidence, and so on. It is therefore essential to evaluate various sinkholes in different depths and sizes to assess the risk of collapse. This paper evaluates the effect of different cavities on Rayleigh-wave propagation and body (P) wave refraction. Rayleigh (R) wave propagation is analyzed according to the classical multi-channel analysis of surface waves (MASW) method also considering the R-wave backscattering. Synthetic seismic traces are computed by means of finite element modeling (FEM) for cavity and intrusion at different depths and sizes. Furthermore, field acquisition data is used to verify the detection effect of a cavity on R- and P-waves. The results show that the presence of backscattered R-waves and the changes in the R-wave velocity spectrum can help in cavity identification. Additional possible evidence is represented by significant changes in the refraction travel times over the cavity location. It can be concluded that the field data are in good agreement with the synthetic, and it could be effective to consider the results of both R- and P-wave analysis in order to efficiently identify the cavities.