Dip-Moveout Correction and Prestack Migration Exercises

Series Investigations in Geophysics Öz Yilmaz http://dx.doi.org/10.1190/1.9781560801580 ISBN 978-1-56080-094-1 SEG Online Store

Exercise 5-1. Consider the application of DMO correction to data referred to a floating datum represented by a smooth form of an irregular topographic surface and data referenced to a flat datum below. Which DMO correction would have more effect on the data?

Exercise 5-2. Refer to Fowler’s velocity-independent prestack migration technique for migration velocity analysis described in migration velocity analysis. Suppose you have transformed the prestack data from offset to velocity space using 30 constant velocity values from 2000 m/s to 4900 m/s using an increment of 100 m/s. Can you create additional constant-velocity panels such that the increment is 50 m/s by poststack migration rather than prestack migration or trace interpolation? If so, what velocity would you use for poststack migration to create the panel for 3050-m/s velocity.

Exercise 5-3. Derive Bancroft’s equivalent offset equation (E-72b) from the nonzero-offset traveltime equation (E-67).

 ${\displaystyle h_{e}^{2}=y^{2}+h^{2}-{\frac {4y^{2}h^{2}}{v^{2}t^{2}}},}$ (E-72b)

 ${\displaystyle vt={\sqrt {(y+h)^{2}+z^{2}}}+{\sqrt {(y-h)^{2}+z^{2}}},}$ (E-67)

Exercise 5-4. Suppose you have two events with conflicting dips of the same magnitude, but in opposite directions, associated with a reflector within a fault block and the fault planes itself. Can these two events be distinguished on a velocity spectrum computed from a CMP gather before DMO correction at a location just above the surface point where the two events intersect one another?