84 Seismic Imaging • 48 channels; • 1 m spacing. – Receivers in borehole 161: • triaxial geophone tool (Geolock H, CGG VSP tool) anchored, thus less sensitive to tube waves; • band range 10-150 Hz. 3.3.2.2 Seismic data It should be noted that the hydrophones recorded the pressure disturbance in the borehole fluid and the geophones the vector wave field at the borehole wall, since the shot was simultaneously recorded by two receiver tools with sensitivity to different physical quantities. Figure 3.18 (a) shows the hydrophone data, dominated by down-going S waves, S-S and S-P reflections; while P-P and P-S reflections are absent. Figure 3.18 Hydrophone data. (a) Showing the different seismic arrivals in the raw data after tube-wave filtering. Note the absence of P-P and P-S reflections and the presence of strong down-going S-wave arrivals. (b) Subset data used as input data for the tomography. Adapted from Beydoun et al. (1989).
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