Abstract：3-D data prestack migration consists two major steps:3-D DMO stack using constant velocity,and 3-D data migration using constant velocity. In the first part,by using a given velocity,seismic data in offset space are mapped into DMO velocity space to form stacked energy at the DMO velocity where layer dip effect has been removed desirably. 3-D data migration using constant velocity is made separately at each DMO velocity data volume,which thus eliminates influence of reflection point location upon velocity. 3-D DMO stack velocity trace gather and 3-D prestack migration velocity trace gather can be obtained respectively after processing of the two steps. Then the two data volumes separately undergo 3-D velocity analysis and 3-D wave field image to have 3-D DMO velocity field,3-D DMO stack section,3-D prestack migration velocity field,and 3-D prestack migration section.
