Parsimonious 2-D poststack Kirchhoff depth migration

Efficiency of Kirchhoff migration can be much improved by using slope infor mation from the seismic section to estimate the incident wave directions. R ay tracing is performed only back along the incident wave directions and so is much reduced. Unlike in conventional Kirchhoff implementations, there i s no need to build traveltime tables, so relatively little memory and input /output use are required. Compression of the input data and restricting the contribution of each time sample to the image to lie within a Fresnel zone of its ray path further reduces the computation time. Synthetic and field data tests show that the new algorithm is about 30 times faster than tradit ional Kirchhoff migration for 2-D post-stack data. The main structural feat ures may be imaged very quickly at the expense of some details. There is a tradeoff between speed and image quality; the optimal compromise is impleme nted by the choice of migration parameters.