An amplitude-preserving migration aims at imaging compressional primar
y (zero-or) non-zero-offset reflections into 3D time or depth-migrated
reflections so that the migrated wavefield amplitudes are a measure o
f angle-dependent reflection coefficients. The principal objective is
the removal of the geometrical-spreading factor of the primary reflect
ions. Various migration/inversion algorithms involving weighted diffra
ction stacks proposed recently are based on Born or Kirchhoff approxim
ations. 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 imag
ed are described a priori by the zero-order ray approximation. The aim
of removing the geometrical-spreading loss can, in the zero-offset ca
se, be achieved by not applying weights to the data before stacking th
em. This case alone has been implemented in this work. Application of
the method to 3D synthetic zero-offset data proves that an amplitude-p
reserving migration can be performed in this way. Various numerical as
pects of the true-amplitude zero-offset migration are discussed.