Apparent AVA effects of fine layering

Abstract

The fine layering of the earth’s subsurface causes apparent amplitude‐variation‐with‐angle (AVA) effects in seismic reflection data. One can distinguish between reflection‐ and propagation‐related apparent AVA effects: the reflection of a package of thin layers is accompanied with angle‐dependent wavelet interference, whereas propagation through finely layered media causes angle‐dependent wavelet dispersion. Obviously, both types of apparent AVA effects hinder AVA inversion for the elastic parameters. Due to the band limitation of the seismic data, the reflection‐related interference effects cannot be removed. However, they can be equalized for all propagation angles by applying an angle‐dependent filter in the imaging step in angle‐dependent migration schemes. The underlying assumption is that the source function is known and that source directivity effects have been compensated prior to migration. The propagation‐related dispersion effects can be compensated for in the downward extrapolation process by means of inverse generalized primary propagators. Angle‐dependent migration, including the above mentioned modifications, yields an angle‐dependent reflectivity section in which the apparent AVA effects of fine layering are suppressed.