Case A 



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Case B 



Case C 



Iso-velocity Surfaces 



Ray Path 



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Figure 578. Several possible dispositions of iso-velocity surfaces with respect to 

 reflecting horizons and associated ray paths for normal ray. Case A — Iso-velocity 

 surfaces all horizontal. Case B — Iso-velocity surfaces parallel to reflecting hor- 

 izons. Case C — Iso-velocity surfaces dipping as a function of depth. Case D^ 

 Iso-velocity surfaces at an angular unconformity. 



