LISPB–III. Upper crustal structure of northern Britain

Interpretation of upper crustal data obtained during the LISPB seismic experiment reveals the velocity structure of the pre-Caledonian basement in northern Britain. Lewisian-like basement with a relatively high seismic velocity (> 6.4 km/s) extends from the Caledonian foreland into the Midland Valley and probably terminates at the Southern Uplands fault. To the south, beneath northern England, the basement has a lower velocity (< 6.3 km/s). We suggest that a horizontal discontinuity may exist in the pre-Caledonian basement between the Southern Uplands fault and the Stublick Line though we cannot yet determine the exact nature of this discontinuity.