A compilation and regional interpretation of the northern North Sea gravity map

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Abstract
A Bouguer anomaly map of the northern North Sea between the Shetland Islands and Norway has been compiled based on four different data sources. The gravity effect of the Devonian to recent sediments was calculated along six published seismic profiles crossing the area and a regional gravity anomaly map produced on the assumption that the sedimentary basin structure is two dimensional. Regional consideration of the gravity field revealed the presence of a mass excess beneath the low-density sediments within the Viking graben. This high-amplitude, long-wavelength anomaly is explained by thinning of the crust from 30 km beneath the flanks to 10 km beneath the centre of the graben, excluding the thickness of the sediments. Crustal thickness along the profiles was derived using the regional gravity field and from this a contour map of the Moho was produced. Predictions obtained from the gravity data confirm the crustal structure derived so far from seismic experiments in the North Sea. For comparison a three-dimensional model of crustal thickness was constructed and a second contour map of the Moho was produced. The Moho contour maps derived from the two-dimensional and three-dimensional models show close agreement, demonstrating that a two-dimensional approach is justified in this case.