True amplitude elastic Gaussian beam imaging of multicomponent walkaway vertical seismic profiling data

摘要

We develop the true-amplitude prestack migration of multicomponent data based on the use of elastic Gaussian beams for walkaway vertical seismic profile (VSP) acquisition systems. It consists in a weighted summation of multishot data with specific weights, computed by tracing elastic Gaussian-beams from each imaging point of the target area towards the sources and receivers. Each pair of beams may be connected with either a pair of P-rays (PP-image) or the P-ray towards sources and the S-ray to receivers (PS-image) and is uniquely determined by dip (the angle of the bisector between the rays and the vertical direction) and opening (the angle between the rays) angles. Shooting from the bottom towards the acquisition system helps to avoid well-known troubles, in particular multipathing for the imaging conditions in complex velocity models. The ability to fix the dip angle and implement summation over opening angles leads to the so-called selective images that contain mostly interfaces with desired slopes. On the other hand, a set of images computed for a range of opening angles by summation over all available dip angles is used as input of an AVO-like inversion procedure for the recovery of elastic parameters.