Prestack Kirchhoff migration and amplitude accuracy

Abstract

Prestack Kirchhoff migration is a successful seismic imaging method, commonly used in exploration seismology. Amplitude analysis and AVO attributes are also a common part of exploration seismology; hence the amplitude integrity of prestack Kirchhoff migration is an important issue. Accurate amplitudes do not naturally fall out of Kirchhoff migration. Three corrections must be computed and applied to the migration operator to ensure accurate amplitudes. First, an anti-alias filter must be applied to ensure that residual operator noise is not created. The anti-alias filter can affect the amplitudes of both flat and dipping events. Next, a derivative filter is applied to ensure that the wavelet phase and frequency content are preserved after migration; this filter does not affect the migrated amplitudes. Finally, most of the amplitude corrections come from ``true-amplitude' weights that are applied to the migration operator. Accurate true-amplitude weights are costly to computeand may even not be worth the effort because of potential instability. In practice, various approximate weights are normally applied, resulting in migrated amplitudes that are usually more accurate than those obtained from conventional processing.