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The orientation of crustal stresses in the North Sea basin and their geological origin

Cowgill, Simon Mark; (1995) The orientation of crustal stresses in the North Sea basin and their geological origin. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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The crustal stress field is a fundamental, first order geophysical property which is intimately related to tectonic processes and provides one of the most effective demonstrations of the Earth's dynamic behaviour. It is generally assumed that the far-field stresses affecting stable intraplate regions result from forces acting on the boundaries of tectonic plates. Previous work has suggested that throughout Western Europe these forces combine to produce a broadly consistent NW-SE maximum compressive stress orientation. For this study, a total of 115,696m of dipmeter data from 115 boreholes have been acquired from a number of oil companies and the former U.K. Department of Energy. The study presented here is the most comprehensive of its kind to date for the North Sea. The data were analysed using an extension to the WELLOG borehole log analysis package developed at the British Geological Survey (BGS). When combined, the data illustrate that the breakout directions within the area are relatively heterogeneous; the mean orientation of minimum horizontal stress is 053°/233° ±25°. This is very similar to the minimum stress direction of 054°/234° ±11° determined for boreholes on the U.K. mainland by the BGS. There is often good agreement between breakout orientations within particular geographical domains, for example in the Southern North Sea basin. However, the data also show that there are significant variations in orientation between different domains throughout the North Sea region. Furthermore, a technique has been developed whereby breakout orientations from individual chronostratigraphic intervals can be compared throughout the region. Use of this technique has shown that the history and age of the rock formation has a profound effect on breakout orientation. It is highlighted that the stress distribution within the North Sea Basin has been controlled throughout time by the reactivation of ancient zones of weakness within the crust and that the superimposition of local geological structure and the effects of palaeostress fields onto the present day tectonic stress field control the orientation of the breakouts described here. It is also apparent that the pre-Jurassic 'basement' rocks show closely related orientations to the rest of Europe whereas the 'basinal' rocks exhibit much more variability which appears to be related to intermediate scale structures within the basin. Finally, stress trajectory modelling has been undertaken across the North Sea Basin for each geographic domain and each chronostratigraphic interval in order to better visualise breakout orientation data and to infer the principal stress axes throughout the area with special reference to those areas containing few breakout measurements.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The orientation of crustal stresses in the North Sea basin and their geological origin
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Applied sciences; Basin, Crustal; Geological; Orientation; Origin; See; Stresses
URI: https://discovery.ucl.ac.uk/id/eprint/10100898
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