Some remarks concerning seismic reflection tomography and velocity analysis

Summary During the last few years seismic reflection tomography has received an increased interest, particularly in connection with offshore oil exploration. The aim of this paper is to provide some basic insight into the theoretical possibilities and limitations of reflection tomography for determining the subsurface velocity structure. Ignoring ray-bending in the overburden, the depth to a flat reflector can be recovered if the slowness function is linear at each fixed depth. A local inhomogeneous region can be reconstructed using reflection traveltimes for a dipping horizon. Making use of ray-bending, a laterally homogeneous structure could, in theory, be determined. In practice, it is possible to obtain the depth(s) to the reflecting horizon(s) and a (piece-wise) linear approximation to the true velocity-depth curve. An inversion procedure based on a parameterization involving velocity gradients is used to achieve this.