Seismic reflection and gravity investigations of the 'Widmerpool Gulf' in the east Midlands, with a study of linear seismic sources and data processing techniques involving computer graphics.

摘要

The gravity anomalies in the vicinity of the Widmerpool Gulf display a strong negative trend, which is best fitted by a third degree surface. This trend is attributed to the development of thick conglomeratic and quartzitic materials, probably of O.R.S and/or Lower Palaeozoic age. The "residual" anomaly is strongly related to variations in depth to the upper surface of the Carboniferous Limestone. Due to partial continuity of sediments along the northern boundary of the gulf, the definition of the gulf in this region is not reflected in the gravity field as strongly as that at the southern boundary. A N - S seismic reflection survey shows little relief in the reflectors and a sudden thinning of sediments towards the southern boundary. At seismic stations where depth penetration was sufficient, a strong unconformity between the "basement" rocks and the younger formations is observed on the time cross section. The seismic reflection survey combined with the gravity and magnetic data, suggests that the southern limit of the gulf is faulted probably against intrusive Caledonian rocks. Theoretical and field studies of linear charges, in cord form (Geoflex) indicate that such seismic sources have definite advantages over the single point charges. This is due to their directional properties and their superior power spectral content. The interactive technique provided by computer graphical devices facilitates the exertion of complete control on the running of programmes. Seismic and gravity programmes using this technique were developed and used in this study.