Wednesday 2 May 2018

Earthquakes off the Knapdale coast, Argyll and Bute, Scotland.

The British Geological Survey recorded a Magnitude 2.6 Earthquake at a depth of about 8 km off the east coast of Knapdale, in Argyll and Bute, Scotland, slightly before 7.20 pm  British Summertime (slightly before 6.20 GMT) on Sunday 29 April 2017. This was followed by a second event with a Magnitude of 2.5 in roughly the same place at about 7.15 am British Summertime (about 6.15 am GMT) on Tuesday 2 May. These were not major events, and presented no threat to human life or property, but were felt in Tarbert, Achahoish, Ardrishaig, Minard, Clachan, Tayvallich, Srondoire, Lochgilhead, Portavadie, Colintraive, Isle of Gigha and Dunoon. 
The approximate location of the 29 April & 5 May 2018 Knapdale Earthquaked. 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.
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 the 29 April 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, or if you felt the 2 May event, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.
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