Multicomponent least-squares Kirchhoff depth migration

• Author / Creator

  Safron, Landon C

• Conventional seismic migration operators produce an image that suffers from low resolution, sampling artifacts, and poorly balanced amplitudes. An improved image can be obtained by casting migration as a least-squares optimization problem in which the goal is to minimize the difference between the predicted synthetic data and the true observed data. This thesis aims to expand the technology surrounding least-squares Kirchhoff depth migration. First, an anti-aliased forward/adjoint Kirchhoff operator is derived for performing seismic modeling and migration. The anti-aliased Kirchhoff operator utilizes a triangular filter that can be efficiently customized on-the-fly. Unlike alternative Kirchhoff operators, the anti-aliased Kirchhoff operator proposed in this thesis is well-suited for least-squares migration because only one copy of the data is required to be produced and stored. Second, the importance of regularizing the least-squares cost function is discussed, and a preconditioning strategy for promoting lateral continuity within common image gathers is reviewed. Since the preconditioner promotes stable features in the model, the eigenvalue distribution of the operator is improved, thereby increasing the rate-of-convergence of conjugate gradients. Lastly, a new cost function is proposed for performing converted wave least-squares depth migration in the presence of S-velocity errors. Due to the low signal-to-noise ratio and strong aliasing of converted waves, S-velocity models are typically less accurate than P-velocity models; consequently, PP seismic images are typically more accurate than PS seismic images. The proposed converted wave migration cost function exploits this observation by registering the PS image volume with the presumably correct PP image volume. The new converted wave cost function is found to be an improvement over the conventional cost function in terms of the accuracy of the image and the flatness of the common image gathers. Moreover, the registration strategy allows the true depths of the converted wave reflectors to be recovered, despite the presence of errors in the S-velocity model.

• Subjects / Keywords

  • Kirchhoff migration
  • Least-squares migration
  • Wavefront construction
  • Seismic migration
  • Seismic imaging
  • Multicomponent
  • Seismology

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R35Q4S212

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.