The acquisition parameters are: Array offset of 50 m; time sampling interval of 16 ms; 256 samples; distance sampling of 10 m; 47 traces; recording duration 4.096 s.
Figure on the left shows the vertical component Z. It is possible to see a refracted P-wave, a reflected P-Wave and two surface waves which have a very strong energy.
On the horizontal component ( figure on the right), we mainly see the two surface waves.
The surface waves are Rayleigh waves: a fast Rayleigh wave and a slow Rayleigh.
The Slow Rayleigh wave has the strongest energy.

The aim of the study is to select the slow surface wave either for analysis or to eliminate it. This wave is fairly visible on trace 23 from 1.5 s onwards.

The example shows:

• trace 23 (selected first),
• polarisation of the slow wave of the selected trace,
• the two initial components (t, x section).

The first step of the processing is to isolate the wave on a single component. The processing works in 2 steps:

• Reduction of the dispersion by applying a phase shift which render the polarisation as linear as possible.
• Projection of the selected on a single component by rotation.

The quality of processing is evaluated on selected traces ( here trace 23).
The values of the rotation and the phase shift have to be refined in such a manner that the slow wave is only present on one component.
In this conditions, we can see that, on this section, the polarization of the wave is stable in distance and that this wave was well isolated.