Reliable seismic depth migrations require an accurate input velocity model. Inaccurate velocity estimates will distort point diffractors into smiles or frowns on a depth section. For both poststack and prestack migrated sections, high velocities cause deep smiles while low velocities cause shallow frowns on migrated gathers. However, for prestack images in the offset domain, high velocities cau...

This paper investigates the applicability of prestack Stolt residual migration when the original image is obtained using an arbitrary velocity model. At its origin, the method is based on an assumption of constant velocity. However, its formulation for depth-migrated images involves a ratio of the reference and target velocities; therefore, for residual migration it is completely irrelevant if ...

Nonlinear reverse-time migration is a modified reverse-time migration that accounts for the nonlinear relation between seismic data and model in order to image multiply scattered waves including multiples. The illumination of multiply scattered waves yields a representation of the Earth’s subsurface that is more sensitive to model parameters, which allows for advanced seismic interpretation. Th...

In areas with structurally complex geology, tomographic velocity analysis is required to estimate velocities. This paper describes a tomographic velocity analysis algorithm which uses planewave synthesis imaging as a prestack migration. In reflection tomography, prestack migration is required for both event picking and traveltime error computation. Traveltime errors are often measured in the fo...

Shot-geophone migration, commonly accomplished using wavefield depth extrapolation (“survey sinking”), has a two way reverse time realization as well. The reverse time version permits imaging of overturned reflections. Shot-geophone migration differs from other prestack migrations in the definition of the prestack image volume which it creates. This difference is most clearly seen by identifyin...

In areas of complex geology, migration-velocity estimation should use methods that describe the complexity of wavefield propagation, such as focusing and defocusing, multipathing, and frequency-dependent velocity sensitivity. Migration-velocity analysis by wavefield extrapolation has the ability to address these issues because, in contrast to ray-based methods, it uses wavefields as carriers of...

Whales migrate long distances and reproduce on a finite store of energy. Budgeting the use of this limited energy reserve is an important factor to ensure survival over the period of migration and to maximize reproductive investment. For some whales, migration routes are closely associated with coastal areas, exposing animals to high levels of human activity. It is currently unclear how various...

Isochron rays are lines perpendicular to isochrons, which represent surfaces of constant two-way traveltime. The image of a temporal sequence of seismic impulses is a sequence of isochrons in depth. The later the time impulse the deeper the isochron. The term isochron ray arises from an analogy between the isochron “movement” and the wave propagation. While isochrons behave as wavefronts, its p...

We demonstrate a method for 2D velocity estimation in complex media characterized by triplicated ray fields. Due to multipathing, Migration Velocity Analysis (MVA) principle has to be revisited, requiring in particular the use of Common Angle Gathers (CAGs) instead of the classical common offset panels. For the inversion itself, locally coherent events are automatically picked in the prestack d...