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Title: Long-term evolution of normal fault systems : controls on the development and evolution of extensional structures in the neotectonic Kenyan Rift, East Africa
Author: Dunningham, Jonathan P.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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Differential GPS, which can provide a positional accuracy of ±4cm in terms of latitude and longitude and ±8cm in terms of fault elevation, was used to survey the dimensions of normal fault blocks in the field. In general, positional data were collected every metre along the crest and base of each fault scarp and, where possible, along lava flow contacts. Such data, when combined with 40Ar/39Ar ages determined form the syn-tectonic lava flows, were used to build up a detailed, quantitative, growth-history of faulting in four field localities; two at the centre and two at the eastern margin of the Kenya Rift. Extensional faulting in the South Kenya Rift appears to have been a very episodic process, expressed as: i) an early phase of rapid vertical fault displacement (up to ~6mmyr-1) that resulted in the formation of a train of discrete, ‘bell-shaped’, fault blocks with relatively large fault displacement/length (d/L) ratios (~0.05-0.07), prior to, ii) fault growth at much lower displacement rates (0.3-0.7mmyr-1), characterised by linkage of the pre-existing fault train to form a single fault with a lowered d/L value (~0.01). The observed reduction in fault displacement rates and d/L value may result from down-dip fault interaction with vertical strength contrasts in the volcanic lava pile or, on a more fundamental scale, the base of the effective elastic thickness (Te). Fault development is also likely to be influenced by the effects of magmatism, since periods of increased fault activity often occur subsequent to renewed phases of rift volcanism and possible dyke emplacement. Episodic fault-growth could therefore be explained by tectono-magmatic cycling within the South Kenya Rift. On a large scale, there is evidence for a progressive migration of strain towards the centre of the rift over the past 2Myr.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available