10 Questions
In the context of seismic anisotropy, what is relevant for the flatness of the gather?
If
What is the primary goal of velocity analysis in seismic data processing?
To ensure the flatness of the gather
Which type of anisotropy is commonly associated with seismic data processing?
VTI anisotropy
What is the purpose of linearized tomography in seismic imaging?
To create a detailed image of the subsurface
What is the relationship between the phase velocity and the group velocity in seismic anisotropy?
They are related by the parameter If
What is the primary application of reflector-driven regularizers in seismic imaging?
To create a detailed image of the subsurface
What is the significance of the parameter in seismic anisotropy?
It affects the flatness of the gather
What is the primary challenge in seismic anisotropy?
Handling the unexpected
What is the significance of Lipari et al. (2017) in seismic imaging?
It presented a new approach to regularized tomographic inversion
What is the primary goal of seismic to well-marker calibration?
To ensure accurate time to depth conversion
Study Notes
Phase Velocity and Group Velocity
- Phase velocity is useful for computing the solution of the wave equation when dealing with plane waves, and Snell's law depends on phase velocity.
- Group velocity is necessary for tracing rays and computing travel times in anisotropic media and can be computed from phase velocity.
VTI Anisotropy
- Velocity is described by 3 parameters: Vz (vertical velocity), δ (controls velocity for medium-small angles), and ε (controls velocity for large angles).
- For small ε and δ (weak anisotropy), velocity can be described by Vz, δ, and ε.
Vertical/Tilted Transverse Isotropy (VTI | TTI) Parametrization
- VH and VN are velocities related to Vp0 (axis velocity) through δ and ε.
- δ affects velocity near the symmetry axis direction, reducing misties and improving depth positioning.
- ε corrects for flattening of seismic events and focusing, and is related to the difference between vertical and horizontal propagation velocities.
Velocity Analysis
- Velocity analysis involves linearized tomography and is affected by traveltime, which is sensitive to velocity but blind to some velocity variations.
- Uncertainty in velocity analysis can lead to different geometries after migration.
Tomographic Uncertainty Analysis
- Input data includes semblance, stack, and CRP (Common Reflection Point) gathers.
- After velocity perturbation, the same traveltime (CRPs remain flat) but different geometries are obtained.
- Uncertainty in velocity affects the final result, and what is unknown can have a greater impact than what is known.
Imaging Uncertainty
- Traveltime measures a reflection traveltime and is mostly sensitive to velocity.
- Traveltime is blind to some velocity variations, and it is possible to tell something about the shape of velocity variations but not the scale.
Other Concepts
- Reflector-driven regularizers can be used to incorporate geological constraints in tomographic inversion.
- Seismic-to-well-marker calibration is necessary for accurate depth conversion.
- Normal moveout in VTI media is affected by anisotropy and is relevant for the flatness of the gather and time-to-depth conversion.
This quiz covers the concepts of phase velocity and group velocity in seismic waves, and their application in anisotropic media.
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