3-D TRUE-AMPLITUDE FINITE-OFFSET MIGRATION

Compressional primary nonzero offset reflections can be imaged into th ree-dimensional (3-D) time or depth-migrated reflections so that the m igrated wave-field amplitudes are a measure of angle-dependent reflect ion coefficients. Various migration/inversion algorithms involving wei ghted diffraction stacks recently proposed are based on Born or Kirchh off approximations. Here a 3-D Kirchhoff-type prestack migration appro ach is proposed where the primary reflections of the wavefields to be imaged are a priori described by the zero-order ray approximation. As a result, the principal issue in the attempt to recover angle-dependen t reflection coefficients becomes the removal of the geometrical sprea ding factor of the primary reflections. The weight function that achie ves this aim is independent of the unknown reflector and correctly acc ounts for the recovery of the source pulse in the migrated image irres pective of the source-receiver configurations employed and the caustic s occurring in the wavefield. Our weight function, which is computed u sing paraxial ray theory, is compared with the one of the inversion in tegral based on the Beylkin determinant. It differs by a factor that c an be easily explained.