The British Geological Survey recorded
a Magnitude 1.9 Earthquake at a depth of 6 km, roughly 15 km to the southwest of the island of Jersey in the Channel Islands slightly before 0.20
am British Summertime (slightly before 1.20 am GMT) on Friday 22 September 2017. Although large for the area, the quake was still to small to
present any threat to human activity, and there were no reports of any
damage or injuries relating to this event.
The approximate location of the 22 September 2017 Jersey Earthquake. Google Maps.
The
precise cause of Earthquakes around 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.
Simplified diagram showing principle of glacial rebound. Wikipedia.
Glacial
rebound seems an unlikely cause of Earthquakes beneath the Channel
Islands, an area that was never glaciated, but this is not entirely the
case. The northwest of Scotland is rising up faster than any other part
of the UK, but the Earth's crust onland in the UK is fairly thick, and
does not bend particularly freely, whereas the crust beneath the Channel
is comparatively thin and more inclined to bend under stress. Thus
uplift in Scotland can cause the entire landmass of Great Britain to
pivot, causing movement in the rocks beneath the Channel.
Map showing areas of the British Isles currently rising or sinking as a result of glacial rebound. Wikipedia.
Witness
accounts of Earthquakes can be useful to geologists trying to
understand the processes that cause them and the rocks beneath the
surface. If you felt this quake (or if you were in the area but did not
feel the quake, which is also useful information) then you can report it
to the British Geological Survey here.
See also...
Follow Sciency Thoughts on Facebook.
