Seismicity and seismic hazard, Cainozoic of north-east Scotland
|Merritt, J W, Auton, C A, Connell, E R, Hall, A M, and Peacock, J D. 2003. Cainozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, sheets 66E, 67, 76E, 77, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland).
Contributors: J F Aitken, D F Ball, D Gould, J D Hansom, R Holmes, R M W Musson and M A Paul.
Seismicity and seismic hazard
The area covered by this memoir is remarkable in that it is more or less completely free from earthquakes. This is equally true of both the modern period (i.e. from 1970 onwards) for which there are good instrumental records available of small events, and for the historical period for which earthquakes are known principally from written descriptions. The published UK earthquake catalogue (Musson, 1994), which concentrates on events larger than magnitude 3 ML (Richter Local Magnitude), contains no earthquakes at all for this area, onshore or offshore. Because of the cultural and historical importance of Aberdeen, the availability of historical records is relatively good and it is quite clear that the absence of reported earthquakes represents a real absence of seismicity and not just a data gap. One can estimate, from a knowledge of the historical sources, that there certainly have been no significant earthquakes along the east coast of this area since at least 1750, and along the north coast since about 1800.
Examination of the BGS instrumental database (Walker, 1998) reveals a very few small events, imperceptible except to instrumental recording. These include an event of magnitude 1.4 ML about 10 km east of Elgin on 11 April 1985, and one of magnitude 2.0 ML offshore, about 23 km north of Rosehearty, on 24 June 1980. This is earthquake activity at a trivially low rate, even by the intraplate standards of the UK.
The reason why the east coast of Scotland should be so much less seismic than the west coast remains obscure. It has been noted that the locus of Scottish seismicity correlates rather closely with the distribution of maximum ice load during the last glacial advance (e.g. Musson, 1996), but this is at best only a partial explanation.
There are records of earthquakes having been felt in this area, going as far back as the turn of the 16th century. However, these have all been the distant effects of large earthquakes occurring elsewhere, principally in the Inverness area, around Comrie, Perthshire, and in the North Sea (especially the Viking Graben area). The Comrie earthquake of 8 November 1608 was felt strongly in Aberdeen, and caused some alarm. The local clergy attributed the earthquake to God’s wrath at salmon fishing being conducted on the River Dee on the Sabbath. The Inverness earthquakes of 13 August 1816 and 18 September 1901 were felt throughout the whole of the area in question, at intensities between 4 and 5 EMS (European Macroseismic Scale).
Particular mention should be made of the Viking Graben earthquake of 24 January 1927 (Musson et al.,
1986). This earthquake had a magnitude of 5.7 ML and was felt over a wide area of eastern Scotland and western Norway; in the UK the effects were strongest in the Buchan area (intensity 5 EMS). Very slight damage was caused at Peterhead. One ceiling in the southern part of the town was damaged and a concrete wall at nearby Keith Inch was said to have been cracked by the shock. These two single instances seem to be the only cases of earthquake damage ever recorded in the whole area.