Anti-aliased Kirchoff migration

Abstract

Discrete space-time aliasing of Kirchhoff migration images arises when the migration operator summation trajectory is too steep for a given seismic trace spacing and frequency content. This operator aliasing is independent of data aliasing, and can seriously degrade the focusing quality of subsurface reflectivity images, especially in the presente of large reflector dip and sparse or irregular 3-D acquisition geometries. We have developed a method based on local time- and dip-variant temporal filtering to suppress Kirchhoff migration operator aliasing. In a numerically efficient implementation, we apply local N-point anti-aliasing triangle filters as three-point filter operations after a step each of causal and anticausal temporal trace integration. Our approach is very conservative in its memory requirements, as demonstrated by a 3-D implementation on a massively parallel Connection Machine CM-5. We compare our new anti-aliased Kirchhoff migration to a conventional aperture-weighted Kirchhoff migration, in applications to both 2-D and 3-D marine seismic data. The results indicate that our anti-aliasing method enhances the resolution of steep salt-sediment interfaces and faults, and suppresses false reflections caused by conventional Kirchhoff migration operator-aliasing artifacts.