Interval velocity analysis using post-stack data has always been a desire, mainly for 3D data sets. In this study we present a method that uses the unique characteristics of migrated diffractions to enable interval velocity analysis from three-dimensional zero-offset time data. The idea is to perform a standard three-dimensional prestack depth migration on stack cubes and generate three-dimensional common image gathers that show great sensitivity to velocity errors. An efficient 'top-down' scheme for updating the velocity is used to build the model. The effectiveness of the method is related to the incorporation of wave equation based post-stack datuming in the model building process. The proposed method relies on the ability to identify diffractions along redatumed zero-offset data and to analyse their flatness in the migrated local angle domain. The method can be considered as an additional tool for a complete, prestack depth migration based interval velocity analysis.
- Dip angle