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Title: Seismic studies of deep structure in the Bristol Channel area
Author: Mechie, J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1980
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In September 1976, seven seismic profiles, 35-90 km long, were completed in the Bristol Channel area. Marine shots using Superflex 200 (Nobels) were fired by RRS John Murray and land recordings were taken on FM magnetic tapes. Analogue replaying and digitizing of the data was subsequently carried out before the digitized data were filtered and plotted in time-distance mosaics by computer. Using planar-layer and time-term methods of interpretation, models for each profile were derived mainly from the first arrival data. In most cases, these models were refined using ray-tracing until a final model for each profile was obtained. A regional time-term analysis of the basal refractor was also carried out, for which data from previous experiments in the area were used and additional data were collected using marine shots and quarry blasts as sources. Top layer velocities measured in this study usually fall within the range r 4.8-5.2 km/s. The Carboniferous Limestone normally has a velocity of 5.1-5.2 km/s. Below the Carboniferous Limestone, the Old Red Sandstone with a velocity of 4.69-4.85 km/s acts as a low velocity layer as does, sometimes, parts of the Lower Palaeozoic succession. In the central South Wales/Bristol Channel area and the Mendips, a 5.4-5.5 km/s refractor was identified which is correlated with a horizon at the top of, or within, the Lower Palaeozoic succession. Under the whole area, except North Devon, a 6.0-6.2 km/s basal refractor was located which is correlated with Precambrian crystalline basement rocks. In general, this refractor deepens southwards beneath the area resulting in a southerly thickening of the pre Upper Carboniferous supra-basement sequence. In North Devon, a 6.2 km/s refractor and a deep reflector were detected, both of uncertain geological significance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available