On Friday 10 August 2012, slightly before 12 noon British Summertime (slightly before 11.00 am GMT), the British Geological Survey recorded an Earthquake in northern Argyllshire, with its center 12 km below the southern shore of Loch Tearnait, measured as 2.3 on the Richer Scale. Earthquakes this small present no real threat to life or property, and are not always felt or recognized, though on this occasion the quake was apparently noted by people as far away as Oban, 20 km to the southeast.
Map showing the location of the 10 August 2012 Earthquake. BGS.
As a rule of thumb Earthquakes become more common in Great Britain as you travel to the north and west, making the west of Scotland the most quake-prone part of the country, and, incidentally, making the people there more likely to recognize quakes when they occur.
The precise cause of Earthquakes in Scotland is often hard to determine, though glacial rebound is considered to play a major role. Until about 10 000 years ago much of Scotland was buried under a thick layer of ice, which pushed the rocks of the Scottish Lithosphere down into the underlying Mantle. This ice has now gone, and these rocks are slowly rebounding, leading to the occasional Earthquake. Scotland is also subjected to tectonic stresses caused by the movements of the Earth's tectonic plates, which can also contribute to Earthquakes. Scotland sits on the western Eurasian Plate, which is slowly being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa from the south. There are also lesser expansion centers within the Eurasian Plate, under the North Sea and the Rhine Valley, which also exert tectonic stresses in Scotland.
Witness statements can help geologists to understand Earthquakes and the rock structures that cause them. If you felt this quake, or were in the vicinity but didn't (which is also useful information) then you can report it to the British Geological Survey here.
See also Earthquake in Nottinghamshire, Earthquake beneath the Kattegat Sea, Isle of Islay shaken by two Earthquakes in two days, Earthquake in the Channel Islands and Earthquakes on Sciency Thoughts Youtube.
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