Integrated wide-angle and near-vertical subbasalt study using large-aperture seismic data from the Faeroe-Shetland region

Acquiring large-aperture seismic data (38 km maximum offset) along a profile crossing the Faeroe-Shetland basin in the North Atlantic enables us to use wide-angle reflections and refractions, in addition to conventional streamer data (0-6 km), for subbasalt imaging. The wide-angle results are complemented and confirmed by images obtained from the conventional near-vertical-offset range. Traveltime tomography applied to the wide-angle data shows a low-velocity layer (3.5-4.5 km/s) underneath southeastward-thinning lava flows, suggesting a 2.5-3.0-km-thick sedimentary layer. The velocity model obtained from traveltime tomography is used to migrate wide-angle reflections from large offsets that arrive ahead of the water-wave cone. The migrated image shows base-basalt and sub-basalt reflections that are locally coincident with the tomographic boundaries. Application of a new multiple suppression technique and controlled stacking of the conventional streamer data produces seismic sections consistent with the wide-angle results. Prestack depth migration of the near-vertical offsets shows a continuous base-basalt reflection and a clearly defined termination of the basalt flows.