Velocity analysis using $AB$ semblance

Field data example

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 $AB$ semblance is shown in Figure 8. Similarly to the synthetic example, the $AB$ 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 $AB$ analysis. The curved reflection event is successfully flattened.

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Figure 7. Input CMP gather after preprocessing. a: trace display, b: wiggle display.

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Figure 8. Residual moveout curvature scans using conventional semblance (a) and $AB$ semblance (b). Black curves indicate automatically picked trends.

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Figure 9. CMP gather from Figure 7 after residual normal moveout correction using trends picked from the $AB$ semblance in Figure 8. a: trace display colored according to the AVO indicator attribute, b: wiggle display.

Velocity analysis using $AB$ semblance