We propose to find the group velocity and the phase change of a Rayleigh . The group velocity is calculated from the delay which would put the envelopes of the seismic traces in phase. After correcting the group velocity, the dispersion is corrected by a phase shift which has to chosen so as to put the seismic traces in phase.

The example shows:

Above: the raw recording,

Below, on the left, choose either:

• the section composed of the envelopes of the seismic traces,
• the recording after the group velocity correction. The value of the group velocity is the value of velocity which flattens the envelopes.

Below, on the right: the recording after the group velocity correction and a phase shift. The value of the phase shift is the value of phase which flattens the Rayleigh wave.

The measurement of the group velocity and the phase shift allows the calculation of the phase velocity and then the dispersion curve for the wave.