Influence of direction on velocity analyses

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Problem 5.20

Given orthogonal dip and strike seismic lines, will velocity analyses at line intersections yield the same values?

Background

Reflecting points on a CMP gather in the dip direction are located updip by distances which increase with offset [see equation (4.11e)] so that a CMP stack smears the data. A DMO correction (Sheriff and Geldart, 1995, section 9.10.2) remedies this.

Solution

A line in the strike direction should yield reliable velocity values, but depths will be slant distances perpendicular to the bed, and reflecting points will be located updip. A commonmidpoint gather in the dip direction will not involve common reflecting points, and measurements will yield erroneous values unless DMO corrections have been made. The velocity analyses will probably yield somewhat different values.

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