The crustal structure of northern England

Abstract

The crustal structure of Northern England was examined, using mainly the refraction technique. A three layer crustal model with interfaces at 0 to 3 km, 12 km, and 27 km was interpreted from the data. The lateral variations in thickness of the sedimentary cover was investigated by measuring Pg travel times from quarry blast sources recorded at mobile stations. The time term method was used to interpret the results and showed that the basement varied from 2i to 3h kin deep within the sedimentary troughs to less than 1km beneath the block regions. The interpretation of apparent velocities of crustal phases across Eskdalemuir and Rookhope arrays, and wide-angle reflections, suggested the existence of a lower crust between 12 and 27 km deep, with a velocity of about 6.5 km/sec. The upper crust (Pg about 5.7 km/sec) showed some evidence of velocity increasing with depth, especially the uppermost part of the granite beneath Rookhope array. A refraction line (N.E.R.L.) recorded the shots of the L.I.S.P.B. project throughout the northern Pennines. This line examined the variation in thickness of the main crustal layers across the principal structural units. It suggested that the Moho was approximately level beneath the region. This indicates that the relative elevation of the blocks was isostatically supported by low density granites. The upper mantle has a Pn velocity of about 8.05 km/sec and the character of the phase suggested a sub-moho structure such as an increase of velocity with depth. The surface wave dispersion of teleseismic events recorded at Eskdalemuir and Wolverton was examined. The interpretation suggested a crust 30 km thick and a shear velocity of 4.55 km/sec for the upper mantle.