Interpretation of a seismic survey of crustal structure in Western Scotland and the Hebrides

Tsoumakos, Petros E. (1986) Interpretation of a seismic survey of crustal structure in Western Scotland and the Hebrides. PhD thesis, University of Glasgow.

Abstract

The Western Isles Seismic Experiment (WISE), a seismic refraction profile, was shot perpendicular to the British Caledonides and runs from the Outer Hebrides (Isle of Barra) to the Scottish mainland (Midland Valley). The aim of the experiment was to determine possible upper crustal velocity variations both vertical and lateral. The ray tracing method is used as the main interpretation technique, as the known geology suggests that the time-term / plus-minus assumptions are frequently violated. This interpretation method has also allowed for the incorporation of existing geophysical and geological controls, in order to compensate for limitations due to the quality and availability of the data and to produce internally consistent models for both the shallow structure (mainly derived from closely spaced airgun data), and the deep structure (from distant explosive-shot data). In the Sea of the Hebrides, interpretation has shown a predominance of typical Laxfordian basement velocities (5.9 - 6.1 km/sec) and a lack of distinguishable lateral variations in the basement velocities, the latter being confined to basin / basement transitions. No granulite layer was detected down to 5 - 7 km depth. The Great Glen Fault zone is shown to have produced, and probably coincides with, a near-vertical low velocity zone which can be traced with a fair degree of certainty down to about 5-6 km depth. That is found to be consistent with geological models of the structure of transcurrent large-scale continental faults, but the structure at greater depth is uncertain due to limitations in the refraction method and data availability. The strong Lewisian / Dalradian and intra-Dalradian velocity contrasts are quantified and are shown to persist to 8 - 10 km depth. The former define an interface that can be seen dipping at about 25 to the SE, while the latter are due to the high velocities (> 6,0 km/sec) of the formations interpreted as the core of the Islay Anticline and the Port Ellen phyllites, compared to those of the Jura quartzite (5.5 km/sec) and the rest of the Dalradian basement (5.3 - 5.8 km/sec). Gravity models based on the seismic interpretation along the profile show a reasonable agreement with the observed field. The variability of the upper crustal structure is finally discussed and compared to that in adjacent areas.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QE Geology
• Colleges/Schools: College of Science and Engineering
• Supervisor's Name: Hall, Dr. J.
• Date of Award: 1986
• Depositing User: Alastair Arthur
• Unique ID: glathesis:1986-76759
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 09 Dec 2019 16:39
• Last Modified: 09 Dec 2019 16:41
• Thesis DOI: 10.5525/gla.thesis.76759
• URI: https://theses.gla.ac.uk/id/eprint/76759