Technical - Basics

GRT is a true-amplitude migration based on ray tracing that computes the reflection response in dependence on sub-surface angle of incidence:

where θ is the inclination angle of the incident ray, measured with respect to the vertical direction, and Ψ is the azimuthal angle. For narrow azimuth data, the azimuthal component is sparsely covered and the migration result R(θ,x) is computed solely in dependence on the inclination angle at sub-surface points x.

Seismic input traces u should not have any amplitude scaling applied prior to GRT migration. GRT internally converts the input traces to versions ũ,t from which the amplitudes are picked according to computed traveltime T(xr,x,xs) between source/receiver and output point xr,x,xs. The weighting factor W and integration weights according to dv make the output R(θ,x) proportional to the reflection coefficient.

The list of features of 3D GRT comprises:

  • Stable implementation for distributed memory clusters of O(100) compute nodes

  • Output of true-amplitude reflection angle gathers

  • Isotropic, VTI, TTI, and orthorhombic velocity models

  • PS wave mode

  • Marine surface, marine OBC, and PP land data

  • Ray-perturbation workflow to enable migration with weakly smoothed velocity models

  • Identification of subsurface azimuth, WAZ migration

  • Output of dip angle gathers for event analysis

  • Dip-focusing and aperture-optimisation