Verification of Rayleigh-wave dispersion characteristics using synthetic microtremors

An attempt to verify the characteristics of experimental Rayleigh-wave dispersion curve from passive microtremor measurements is carried out through synthetic microtremors. As case study, array microtremor measurements were performed at an Alpine site. The average experimental vertical Rayleigh dispersion curves obtained by the f-k spectral method was used to estimate subsoil models by random search (Monte Carlo inversion). Also, the predominant frequency of experimental H/V spectral ratio was calculated to improve the inversion process. Several researchers have reported that the fundamental frequency of theoretical H/V spectral ratio or the predominant frequency of experimental H/V spectral ratio would represent an approximate threshold for the lowest frequency of experimental vertical Rayleigh dispersion curve. However, the highest velocity of the experimental Rayleigh dispersion curve occurred at a frequency higher than the value of the experimental H/V predominant frequency. In consequence, this experimental high velocity would not correspond to the fundamental Rayleigh dispersion curve. For verifying purposes, synthetic microtremors using a similar array to the one used at the site, were calculated for one of the subsoil models estimated through Monte Carlo inversion. The synthetic vertical Rayleigh dispersion curve was in good agreement with the experimental one, verifying the above assumptions.