Abstract

Interpretation of the NSDP (North Sea Deep Profile) regional grid of deep (15 s TWT) reflection seismic data gives an understanding of both the shallow crustal tectonics of the North Viking Graben and their relationship to the lower crustal structure. The three east-west lines show common structural elements along the length of the graben and a uniformity of tectonic pattern not necessarily apparent on shallow 4-5 data. On each of the lines, the major half-graben symmetry of the basin is apparent, as is the crustal rollover on the eastern side of the graben. This fundamental asymmetry has major implications for the distribution of structure and trapping styles on both flanks of the graben.

The Viking Graben is developed on a major, low angle eastward-dipping detachment. This detachment links the faults in the upper crust to the lower crust and eventually to the upper mantle. Extension (the beta factor) in the plane of section on this linked detachment for the Mesozoic basin, may be as high as 3.

The Mesozoic basin developed on the same major structural elements as its Permian and Devonian precursors. Most of the structural elements are probably Caledonian in origin, although they have been extensively modified.

Inversion and strike-slip elements of the basin geometry are apparent from the data and are seen as part of a linked system with the extensional geometry. The oblique tie-line (NSDP 4) shows a considerable component of crustal thinning in a northeast direction, probably due to an oblique, or a subsequent strike-slip opening of the graben.