Patent ID: 7330799

Claim:
A method, using a Rayleigh wave, for establishing a set of dispersion curves characterizing a medium, wherein each dispersion curve is associated to a propagation mode of said Rayleigh wave, the method comprising: deploying on a surface of the medium a plurality of sensors; generating a surface wave in the medium; monitoring with said sensors a propagation of the surface wave for providing a plurality of signals in the time domain, wherein said signals comprise a spectrum of frequencies; determining, from said plurality of signals, and for each of said frequencies, an energy distribution as a function of phase travel time and group travel time, wherein said determining an energy distribution comprises computing a wavelet transform of said signals as a function of said phase travel time and group travel time for providing said energy distribution; identifying a set of said propagation modes of the Rayleigh wave using said energy distribution; establishing, for each identified propagation mode, a dispersion curve using said energy distribution, thereby providing said set of dispersion curves characterizing said medium; and further comprising at least one of: inverting said dispersion curves for determining a profile of shear velocity as a function of a depth in said medium, said inversion comprising reconstituting the shear wave velocity profile that corresponds to at least two of said dispersion curves, wherein said reconstituting comprises adjusting said shear velocity profile such as to minimize an error between a calculated dispersion curve and an experimental dispersion curve, wherein said calculated dispersion curve is calculated with the shear velocity profile and wherein said experimental curve is one of said dispersion curves; inverting said dispersion curves for determining a profile of a Poisson ratio as a function of a depth in said medium, said inversion comprising reconstituting the profile of the Poisson ratio that corresponds to at least two of said dispersion curves; and inverting said dispersion curves for determining a profile of a Poisson ratio and a shear wave velocity profile, both profiles being characteristics of the medium, as a function of a depth in said medium, said inversion comprising reconstituting the profile of the Poisson ratio and the profile of the shear wave velocity that will simultaneously correspond to at least two dispersion curves.