NUMERICAL TESTS OF 3D TRUE-AMPLITUDE ZERO-OFFSET MIGRATION

An amplitude-preserving migration aims at imaging compressional primary (zero-or) non-zero-offset reflections into 3D time or depth-migrated reflections so that the migrated wavefield amplitudes are a measure of angle-dependent reflection coefficients. The principal objective is the removal of the geometrical-spreading factor of the primary reflections. Various migration/inversion algorithms involving weighted diffraction stacks proposed recently are based on Born or Kirchhoff approximations. Here, a 3D Kirchhoff-type zero-offset migration approach, also known as a diffraction-stack migration, is implemented in the form of a time migration. The primary reflections of the wavefield to be imaged are described a priori by the zero-order ray approximation. The aim of removing the geometrical-spreading loss can, in the zero-offset case, be achieved by not applying weights to the data before stacking them. This case alone has been implemented in this work. Application of the method to 3D synthetic zero-offset data proves that an amplitude-preserving migration can be performed in this way. Various numerical aspects of the true-amplitude zero-offset migration are discussed.