A seismic refraction study of the crustal structure of North West Scotland and adjacent continental margin

Abstract

In the summer of 1975, the Department of Geological Sciences, University of Durham, carried out a long range refraction project using explosions fired in Rockall Trough and the Hebridean Shelf areas. Temporary recording stations were situated in the North-west Highlands and Islands of Scotland. The data was supplemented by recordings from the permanent networks of Scotland. Plus-minus, time-term, velocity filtering and particle motion processing methods were applied to the data. Wherever possible, results from gravity and magnetic studies and seismic reflection profiles were used to compliment the interpretations. On the Hebridean Shelf, small sedimentary basins and lateral variations of basement velocity are shown which correlate with earlier gravity and magnetic interpretations. Low average crustal velocities on the shelf, west of the Hebrides, give crustal thicknesses of about 25 km but east of the Hebrides higher average crustal velocities give estimates of about 30 km. A mid-crustal refractor is not clearly observed but may be at a depth of about 18 km on the outer shelf. The Minch area shows large P(_n) time-terms but this does not necessarily signify thickened crust since they may be attributed to velocity anomalies within the crust. Continental crustal thinning and transition to oeanic crust at the Rockall Trough margin takes place over a narrow zone of about 50 km width. Crustal thicknesses in Rockall Trough, at 58 N, are between 7 and 12 km and further north, near Rosemary Bank, are between 12 and 24 km.