21 1. Shear velocity measurement in boreholes 1.2.1 Downhole During a downhole acquisition, the seismic receiver is inside the borehole and the source is on the surface. Alternative configurations can be implemented with a seismic receiver in a cone penetrometer (Seismic Cone Penetration Testing - SCPT) or in a dilatometer (SDMT). In addition, a configuration with two receivers separated by a fixed distance is also possible. Depending on the type of strike on the ground surface (vertical or horizontal), the seismic source can generate a signal containing a maximum of energy in the compression wave (P) or the shear wave (S), see Figure 1.3. Figure 1.3 Typical configuration of a downhole where the shear waves are mainly recorded by horizontal components and the compression wave by the vertical component of the geophone in the borehole (according to SeisImager technical documents, 2013). 1.2.1.1 The acquisition device It is necessary to dissociate the acquisition and analysis of compression waves (P) and shear waves (S).
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