A seismic refraction line across Norfolk

A simple seismic refraction line some 115 km long has been made across Norfolk to provide constraints on the depth to the ‘igneous/metamorphic’ basement. Shots were fired in the Wash and off the coast near Lowestoft and attempts were made to record at approximately 2 km intervals along the line. Recording quality was only fair, resulting in incomplete coverage of the line, and this restricts the quality of interpretation. The results show a refractor of about 6.05 km s −1 revealed over the whole line with no first-arrival evidence of the 4.5–5.5 km s −1 velocity expected from Palaeozoic sediments. Using estimated velocities of 2.4 km s −1 for the post-Palaeozoic succession, 4.5–5.5 km s −1 for the Palaeozoic succession and an estimated sub-crop position of the basement on the sub-Mesozoic floor, models are produced which suggest that the Palaeozoic sediments are no more than 600–1500 m thick at the eastern end of the line, depending on the Palaeozoic velocity assumed.