114 Seismic Imaging Figure 4.20 Example of an elementary cross-spread. Figures 4.21 and 4.22 show the first steps of the processing of the cross spread recorded on line 11 with a 60 m source offset. After amplitude recovery (Figure 4.21, top left) and deconvolution (Figure 4.21, bottom left), the wave separation procedure is applied as follows: • Extraction of the refracted wave by SVD filter (Figure 4.21, top right). • Subtraction of the refracted wave from the initial section to obtain the first residual section (Figure 4.21, bottom right). The residual section shows mainly surface waves with low apparent velocities. • Extraction of the low apparent velocity events by F-K filter (Figure 4.22, top left). • Subtraction of the low apparent velocity events from the first residual section to obtain the second residual section (Figure 4.22, bottom left).
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