Numerical implementation of multicomponent true-amplitude Kirchhoff imaging in two and one-half dimensional v(x,z) media, requires the computation of several ray quantities: traveltimes, slowness, polarization vectors, and geometrical spreading. The purpose of this paper is to show that all of these weighting (Green's) functions can be computed by means of the nonhyperbolic traveltime formula of (Tsvankin and Thomsen, 1994) and (Hake et al., 1984) without any need of ray-tracing, in the case of vertically stratified VTI media. Such models are common in hydrocarbon exploration contexts, with a classical example being that of stratigraphic trap located within a horizontally layered sedimentary sequence. By means of nonhyperbolic traveltime function, we derive explicit approximations for the elastic Green's functions, applicable for multi-component true-amplitude Kirchhoff time and depth migration in vertically inhomogeneous VTI media. Numerical tests with synthetic data from 2D isotropic model show that the images computed by multicomponent true-amplitude Kirchhoff depth migration using explicit approximations of the Green's function compare well with results obtained based on dynamic ray-tracing. We have also succesfully applied the new elastic true-amplitude migration algorithm on 2D-4C OBC seismic data. The main advantage of the method is numerical efficiency rather than high accuracy. It may be of interest for prestack imaging of large data volumes and fast computation of prestack images of multicomponent data. Moreover, the proposed approach is well suited for migration velocity analysis for converted and non-converted waves in anisotropic media, where fast and repeated prestack migration is desired.
Figures & Tables
“This volume contains 25 papers that represent most of the best work in seismic anisotropy in 1998 and 1999. Fracture characterizations and processing of converted waves are the two main topics covered in this volume. They are addressed from both theoretical and practical viewpoints. Also included are papers describing the historical roots of seismic anisotropy.”