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![]() | Velocity analysis using ![]() | ![]() |
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For a field data example, I select a gather already processed by a
seismic contractor. The gather, shown in Figure 7,
exhibits a clear polarity reversal around 3.8 s. The polarity
reversal is the apparent cause of a visible residual moveout
artifact. In order to correct the residual curvature, I apply
semblance-based analysis. The comparison between the conventional and
the
semblance is shown in
Figure 8. Similarly to the synthetic example, the
semblance provides a better indicator of the residual
velocity for the curved event with anomalous
amplitude. Figure 9 shows NMO-corrected gather using a
velocity trend picked automatically from the
analysis. The curved reflection event is successfully flattened.
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gath4
Figure 7. Input CMP gather after preprocessing. a: trace display, b: wiggle display. |
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scan4
Figure 8. Residual moveout curvature scans using conventional semblance (a) and ![]() |
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nmo4
Figure 9. CMP gather from Figure 7 after residual normal moveout correction using trends picked from the ![]() |
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![]() | Velocity analysis using ![]() | ![]() |
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