Tuesday, 2 June 2015

Yorkshire stuck by two Earthquakes in under ninety minutes.

The county of North Yorkshire in northern England was struck by two Earthquakes on Saturday 30 May 2015, according to the British Geological Survey, the first occurring slightly before 7.10 pm British Summertime (silghtly before 6.10 pm GMT) to the northwest of the town of Skipton in the southern Yorkshire Dales National Park, having a Magnitude of 1.7 and occurring at a depth of 7 km. The second occurred to the west of the town of Richmond at about 8.20 pm British Summertime (about 7.20 pm GMT) and had a Magnitude of 2.6 and a depth of 11 km. Neither of these events was large enough to present any danger to human life or property, but the second was felt in the village of Crackpot.

The approximate location of the first 30 May 2015 North Yorkshire 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. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic presures tend to build up for longer periods of time between events, so that when they occur more pressure is released.

The approximate location of the second 30 May 2015 North Yorkshire Earthquake. Google Maps.

The precise cause of Earthquakes in the UK can be hard to determine, though it is likely that these two events were related. 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 the first 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, while if you felt the second quake you can report it here.

See also...

The British Geological Survey recorded a Magnitude 1.7 Earthquake at a depth of 4 km in the Kents Bank area of Morcambe Bay, northwest England, at about 5.55 pm...

The British Geological Survey recorded a Magnitude 1.9 Earthquake at an uncertain depth near the village of Wormersley...

The British Geological Survey recorded a Magnitude 1.9 Earthquake at a depth of 10 km about 7 km to the northwest of...

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