An Equivalent Offset time migration for anisotropic data

Abstract

The Equivalent Offset (EO) method of migration is a Kirchhoff prestack method that forms prestack migrated gathers suitable for RMS velocity analysis. All input data, within the migration aperture, is summed into each EO gather. After normal moveout (NMO) correction, stacking completes the prestack migration. The migration can be in time or depth, however the time migration is much faster than a conventional Kirchhoff time migration as no time shifting is required when gathering. Antialiasing filtering, scaling, and NMO are only performed after the gathering has been completed. The EO gathers contain hyperbolic shaped reflection energy with the moveout shaped with RMS velocities. The fold in each bin of the EO gathers is very high, while the noise is very low proving accurate velocity analysis. Anisotropic parameters may be included when forming the EO gathers. A shifted hyperbola technique was used to map the input data to an appropriate offset bin of the EO gather. The moveout in these anisotropic EO gathers is still hyperbolic and conventional velocity analysis will produce the vertical RMS velocity.