Moveout analysis of wave-equation extended images

Conventional velocity analysis applied to images produced by wave-equation migration with a cross-correlation imaging condition makes use either of moveout information from space-lags or of focusing information from time-lags. However, more robust velocity estimation methods can be designed to take advantage simultaneously of the moveout and focusing information provided by the migrated images. Such joint velocity estimation requires characterization of the moveout surfaces defined jointly for spaceand time-lag common-image gathers. Such surfaces estimated for single events (shots) are non-planar but they reduce naturally to the conventional space-lag and time-lag moveout functions. The superposition of those surfaces for many experiments (shots) in a common-image gather forms a shape which can be characterized as a “light-cone” in the lag space. When imaged with correct velocity, the focus of the light cone is located at the correct image depth and at zero spaceand time-lags. When imaged with incorrect velocity, the focus of the light cone shifts both in depth and along the time-lag axis. The characteristics of the light cones are directly related to the quality of the velocity model, thus their analysis provides a rich source of information for velocity model building. Joint migration velocity analysis technique exploiting the entire information provided by the extended imaging condition has the potential to benefit from the combination of the robustness of depth focusing analysis and of the high resolution of conventional semblance analysis.