Friday, 19 December 2014

Magnitude 1.2 Earthquake in Ross and Cromarty, Scotland.

The British Geological Survey recorded a Magnitude 1.2 Earthquake at a depth of 8 km close to the town of Alness in Ross and Cromerty County, Scotland (about 25 km north of Inverness), slightly after 3.45 am GMT on Wednesday 17 December 2014. There is no danger of any damage or injuries from an Earthquake this small, though it may have been felt locally.

 The approximate location of the 17 December 2014 Ross and Cromarty Earthquake. Google Maps.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England. 

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.
Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 
(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.
Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.
See also...
The British Geological Survey recorded a Magnitude 1.0 Earthquake at a depth of 7 km on the southeastern Isle of Skye slightly after 12.30 pm British Summertime...

The British Geological Survey recorded a Magnitude 2.9 Earthquake at a depth of 5 km roughly 10 km to the west of Fort William in Highland County, Scotland, slightly after 7.35 pm British Summertime (slightly after 6.35 pm GMT) on Thursday 3 July 2014. This is a large quake for Scotland, but not dangerous and there are...
The British Geological Survey recorded a Magnitude 1.4 Earthquake at a depth of 2 km in the Torridon Hills of western Ross and...
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