Seismicity, Northern Highlands of Scotland
|Johnstone, G S and Mykura, W. 1989. British regional geology: Northern Highlands of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.|
The north of Scotland has a long recorded history of earthquake activity stretching back to 1597, when on 23 July an earthquake was reported to be felt over most of the area from Ross and Cromarty to Perth. Until recent years, however, the observed pattern of activity has been strongly influenced by population distribution, and it is likely that many events occurring in remote districts have gone unreported.
Using documentary sources to study past earthquakes in Scotland one can loosely discern two main areas of activity north of the Highland Boundary Fault. These are the west coast, from Inveraray and Lochgilphead north to Ullapool, and the Great Glen from Inverness to the vicinity of Invergarry. In addition, a few small events are known from other locations; for example, a major source of seismic activity near Comrie, very close to the Highland Boundary Fault itself, was responsible for many hundreds of earthquakes (most of them small) from 1788 to 1950. The eastern part of the area, the Grampians, and also the extreme north, are almost devoid of seismic activity.
Recent instrumental monitoring confirms the historical pattern, inasmuch as most seismic activity since 1967 has been concentrated on the west coast; relatively few events have been detected east of Spean Bridge or north of Kinlochewe. It is also notable that very little activity has been observed in the Inverness area, despite the occurrence in the past of damaging earthquakes that have affected that city, notably the events of 13 August 1816, and 18 September 1901.
Many of the earthquakes in the west of Scotland detected by BGS instruments are too small to be felt by people. In 1983 nine such events were detected in the north-west of Scotland, and only one felt. The last, which took place on 25 February, 1983, had a small Richter magnitude of 2.2 and was felt weakly at Spean Bridge.