Sub-basalt decoupled walkaway VSP imaging

Walkaway vertical seismic profile (VSP) data acquired in basalt-covered areas can be used to improve knowledge of the sub-basalt structure. A synthetic example and a case study from the North Atlantic (UK) show that elastic two-way downward-continuation migration combined with the stationary-phase principle is well suited to the processing of VSP data. Vector data are processed using decoupled elastic migration algorithms in both isotropic and anisotropic media. To illustrate the value of decoupled imaging equations, conventional PP imaging is carried out on the enhanced VSP data and compared with the decoupled scheme. Decoupled vector migration operates directly on the displacement vector, and uses various wave modes. Downgoing waves are migrated to image basalt lava flows and measure their anisotropy. Upgoing waves are used for high-resolution sub-basalt imaging.