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3D seismic reflection mapping of the Silverpit multi-ringed crater, North Sea

S.A. Stewart^,1 and P.J. Allen²

¹ BP Azerbaijan, c/o Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, UK
² Production Geoscience Ltd, Banchory AB31 5YR, UK

The first comprehensive mapping of the Silverpit multi-ringed crater is presented, based on five adjoining 3D seismic surveys that together provide 78% (216 km²) areal coverage of the structure with spatial and depth sampling of 10 m. The top Cretaceous surface shows an excavated crater 3 km in diameter surrounded by 10–15 concentric ring structures out to a radius of 9.4 km. Seismic sequence stratigraphy and drilled wells indicate the lower age bound is a disconformity spanning 74–54 Ma. The upper bound is Eocene termination of concentric ring fault growth (ca. 45 Ma). The inner rings are extensional faults defining rotated fault blocks that would be considered part of the crater in an impact structure interpretation, giving a final impact crater diameter of 8 km. The outer rings show a surprising variation in style, from graben in the west to compressional structures in the east. This may be explained by postcratering gravity spreading on easterly dipping intra-Cretaceous detachments. Within the crater, the top Cretaceous seismic reflector is disrupted and blocky, but defines a central uplift with a slight crestal depression. Below this uplift, the prominent base Cretaceous seismic reflector shows Jurassic strata rising into a cone 300 m high and 1 km wide, characterized by radial faults. This central uplift within the crater may structurally balance the inner ring fault blocks via a slumping model, but we also identify low seismic velocity in the uplifted Jurassic, so fracturing may have contributed to growth of the central peak. At a radius of 2.5 km, base Cretaceous shows a dish-shaped depression that we interpret as marking either the extent of slumping toward the crater at this structural level or the limit of shockwave-induced porosity collapse. Seismic reflectors above the top Cretaceous excavated crater show differential compaction during the Eocene, accommodated by drape structure plus two conical faults that define narrow ring graben and represent the final phase of crater-related tectonics.

Key Words: impact crater • North Sea • reflection • seismic

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