Principles of Migration Using Kirchhoff's Methods
The ultimate goal of recording seismic data is to recover an image of the geologic structure in the subsurface. Imaging is the most computationally demanding and data-intensive component of seismic processing. Therefore, researchers have spent considerable effort in devising imaging strategies that are effective and that yield accurate images, but that are computationally affordable. The most accurate and most expensive types of migration are those that operate directly on the entire prestack data set; they are called full-prestack migrations. All other imaging methods are designed to approximate full-prestack migration; they aim to achieve the same image accuracy but at a fraction of the computational cost. In this chapter, the main characteristics of 3D prestack migration are analyzed. An understanding of these features is important if one is to determine when full-prestack migration is required and to evaluate its several available approximations.
Imaging of the subsurface is the result of two processing steps that are tightly connected — velocity estimation, and migration. Migration focuses the data and produces an image of the subsurface. However, adequate information on propagation velocity is needed for migration to focus the data properly and to produce the correct image of strata at depth. This chapter discusses the strong dependence of prestack migration on accuracy of the velocity function. In particular, these topics are discussed: principles of time migration and depth migration, and their differences with respect to reliability of the velocity-function estimates that each of them requires.
The link between migration and velocity estimation is provided