Great Glen Fault
The Great Glen Fault is a long strike-slip fault that runs through its namesake, the Great Glen, from coast to coast in Inverness-shire and on to County Donegal. The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years.
The fault appears clearly both as a line on the map and physically on the ground: in this deep, straight slice though the land lie Loch Ness, Loch Oich, Loch Lochy and Loch Linnhe. it marks a natural boundary between the North-West Highlands and the ret of the land.
Location
Aligned north-east to south-west, the Great Glen Fault extends further south-west in a straight line through Loch Linnhe and the Firth of Lorne, and then on into north-western Ireland, directly through Lough Swilly, Donegal Bay and Clew Bay as the Leannan Fault. To the north-east the fault connects to the Walls Boundary Fault and the associated Melby Fault and Nestings Fault, before becoming obscured by the effects of Mesozoic rifting to the north of Shetland.[1]
The fault continues on the North American side of the North Atlantic Ocean, but is no longer part of a contiguous fault, as the complete fault was broken when the Mid-Atlantic Ridge formed 200 million years ago. The North American side of the fault runs through the length of north-western Newfoundland as the Cabot Fault (or 'Long Range Fault') and on into the Gulf of St Lawrence.[2] It is at least 300 miles long.
History
The Great Glen Fault has a long movement history. It formed towards the end of the Caledonian orogeny associated with the collision between the Laurentia and Baltic tectonic plates at the end of the Silurian continuing into the Early Devonian (likely age range 430–390 Ma (million years)). The movement at that time was sinistral (left-lateral), the same as the closely related set of faults sub-parallel to the main part of the Great Glen Fault, which include the Strathconon Fault and Strathglass Faults to the northwest and the Laggan Fault, Tyndrum Fault, and Ericht-Laidon Fault to the southeast.[1] The second main phase of movement was during the Carboniferous, this time with a dextral sense.
The exact timing is uncertain, but associated folds within the Devonian are cut by members of the Late Carboniferous to Early Permian dyke swarm. The Great Glen Fault had its final phase of movement during the Late Cretaceous to Early Tertiary. The displacement is estimated to be 64 miles.[3]
Erosion along the fault zone during Quaternary glaciation formed Loch Ness.
The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years which has meant that seismic buffers are built into the Kessock Bridge carrying the A9 road out of Inverness. Fortunately, none of the modern day infrastructure has been affected by the tremors, as the latest one to affect Inverness and the surrounding area occurred in September 1901 and was approximately a 5.0 magnitude quake.[4] In the 19th century, a boat canal known as the Caledonian Canal was dug through the Great Glen; the canal is still used today.
Outside link
- Why There's a Straight Line Through Scotland - YouTube
- Location map: 57°4’48"N, 4°45’36"W
References
- ↑ 1.0 1.1 Stewart, M.; Strachan, R.A.; Holdsworth, R.E. (1999). "Structure and early kinematic history of the Great Glen Fault Zone, Scotland". Tectonics 18 (2): 326–342. doi:10.1029/1998TC900033. Bibcode: 1999Tecto..18..326S.
- ↑ Redfern, Ron (November 2001). Origins: The Evolution of Continents, Oceans and Life. University of Oklahoma Press. pp. 82–83. ISBN 978-0-8061-3359-1.
- ↑ "Great Glen Fault". 2016. http://www.scottish-places.info/features/featurefirst10625.html.
- ↑ Piccardi, Luigi. (2014). Post-glacial activity and earthquakes of the Great Glen Fault (Scotland). Memorie Descrittive della Carta Geologica d’Italia. XCVI. 431-446.
- Dewey, John F.; Kennedy, Michael J.; Kidd, William S.F. (1983). "A geotraverse through the Appalachians of northern Newfoundland". Profiles of Orogenic Belts. Geodynamics Series. 10. American Geophysical Union. http://www.atmos.albany.edu/facstaff/wkidd/Dewey_etal83.pdf.
- Dewey, J. F. (2005). "Orogeny can be very short". Proceedings of the National Academy of Sciences of the United States of America 102 (43): 15286–15293. doi:10.1073/pnas.0505516102. PMID 16126898. Bibcode: 2005PNAS..10215286D.
- Rogers, D. A.; Marshall, J. E. A.; Astin, T. R. (1989). "Devonian and later movements on the Great Glen fault system, Scotland". Journal of the Geological Society 146 (3): 369–372. doi:10.1144/gsjgs.146.3.0369.
- Stewart, M.; Strachan, R. A.; Martin, M. W.; Holdsworth, R. E. (2001). "Constraints on early sinistral displacements along the Great Glen Fault Zone, Scotland: structural setting, U-Pb geochronology and emplacement of the syn-tectonic Clunes tonalite". Journal of the Geological Society 158 (5): 821–830. doi:10.1144/jgs.158.5.821. Bibcode: 2001JGSoc.158..821S.
- Stephenson, D.; Gould, D. (1995). British Regional Geology. The Grampian Highlands (4 ed.). Her Majesty's Stationery Office, London: British Geological Survey.
- Trewin, N. H., ed (2002). The Geology of Scotland. The Geological Society, London.
- John Tuzo Wilson (14 July 1962). "Cabot Fault, An Appalachian Equivalent of the San Andreas and Great Glen Faults and some Implications for Continental Displacement". Nature 195 (4837): 135–138. doi:10.1038/195135a0. Bibcode: 1962Natur.195..135W.
- John Tuzo Wilson (2014). "Post-glacial activity and earthquakes of the Great Glen Fault (Scotland)". Memorie Descrittive della Carta Geologica d'Italia 96: 431–446. http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/memorie-descrittive-della-carta-geologica-ditalia/memdes_96_piccardi2.pdf.