Neotectonics and Palaeoseismicity in North West Scotland

Fenton, Clark Henderson (1991) Neotectonics and Palaeoseismicity in North West Scotland. PhD thesis, University of Glasgow.

Abstract

Detailed field investigation has revealed a number of faults that display late Quaternary movement in the formerly glaciated Highlands of North West Scotland. These include NE-orientated reverse, WNW- to NW-orientated sinistral strike-slip and N- to NNW-orientated dextral strike-slip faults. In all cases movement has occurred along pre-existing basement faults. The faults offset late Quaternary morphological features, including drainage courses, and disrupt late- and post-glacial sediments. Electron Spin Resonance was used in an attempt to accurately age-date the fault movements. Although this proved unsuccessful, this study showed the limitations of using this technique in relation to fault dating studies. Fault movement was accompanied by coseismic ground deformation as shown by the density of seismically-triggered slope failures and seismite soft sediment deformation around the fault ground ruptures. The areal distribution of these deformation features and the dimensions of the associated fault ruptures indicate elevated levels of seismic activity, with events up to Ms 7.0. This is considerably greater than the levels of seismic activity experienced at present. Faulting was associated with a period of rapid isostatic uplift during and immediately following the decay of the last glacial episode, the Main Late Devensian, c. 13,000 years BP. A short-lived glacial readvance, the Loch Lomond Stadial, lasting from c. 11,000 to 10,300 years BP, caused temporary redepression of the crust halting uplift and faulting prior the main period of fault activity post-10,300 years BP. Although the majority of fault movement occurred in the immediate post-glacial period, significant fault movement has occurred as recently as 2,400 years BP. Faulting resulted from the sudden release of glacial loading stresses and tectonic stresses stored during ice-sheet residence. Elevated pore fluid pressure is seen to be important in the timing and sustaining of fault movement outwith the immediate post-glacial period. Such elevated pore fluid pressure also allowed the reactivation of faults that were less favourably orientated with respect to the regional stress field. This evidence for fault movement and seismic activity in the early part of the Holocene is compared with present day seismotectonic activity and used to predict the present day risk of ground rupture and damaging earthquake activity in the UK as a whole. It is proposed that present day crustal movements result from the actions of the NW European regional stress field, the effects of glacially-induced stresses now having decayed to insignificant levels.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Geology, Geophysics, Plate tectonics
• Date of Award: 1991
• Depositing User: Enlighten Team
• Unique ID: glathesis:1991-78344
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Feb 2020 12:09
• Last Modified: 28 Feb 2020 12:09
• URI: https://theses.gla.ac.uk/id/eprint/78344