Seismic refraction experiments between Iceland and Scotland

Abstract

Two reversed seismic refraction profiles, 90 and 120 km in length, located between Iceland and Faeroes, show that the crust of the Iceland-Faeroe Rise is neither typically oceanic nor typically continental. It is of the order of 18 km thick and shows layering similar to that observed on Iceland. Offsets in the travel-time graphs are identified with marked topographic variations in the upper boundary of layer 2.A third profile on the lower flank of the Iceland-Faeroe Rise, to the south-west, shows that the crust thins in this direction. Seismic refraction profiles over and adjacent to a previously located sedimentary basin on the continental shelf west of the Shetland islands, confirm the probable existence of a 3 km thick sequence of Mesozoic-Tertiary strata, and establish that there is a similar thickness of higher velocity, possibly Palaeozoic, rock between this and the met amorphic basement. Seismic refraction and reflection data and gravity and magnetic field measurements obtained from a region close to the south-west coasts of the Shetlands, confirm and locate the southerly extension of the Walls boundary fault. A sedimentary basin is outlined which is 1 to 1.5 km deep and probably of Mesozoic-Tertiary age. In addition, it is concluded that rocks similar to the granite and Walls sandstone of the Walls Peninsular underlie the sedimentary basin and that there is a trough of Old Red Sandstone rocks to the east of Sumburgh Head, south Shetlands.