Determination of the spatial position of the rugged topography surface is the key to the success of the pre-stack depth migration and velocity modeling on relief surface.The floating datum is not only a rugged topography elevation surface,but also defines the rules on which the CMP gathers are used for datum corrections.Analyzed the definition of the floating datum and clarified the physical meaning of the floating datum in general situations.The seismic data and velocity on floating datum can be directly used for topography pre-stack depth migration and velocity modeling under specific conditions.Discussed the situation that the improper use of floating datum data and corresponding RMS velocity in pre-stack depth migration and velocity modeling might result in shifting and distortion of the horizon layers in depth migration results.
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