Two Earthquakes Recorded In the Irish Sea
The Irish National Seismic Network (INSN) has said that today’s earthquakes in the Irish Sea in a region off the
northwest coast of England were most likely the result of glacial rebound, the process whereby stresses built up the
weight of glaciers from the last Ice Age are slowly released.
A magnitude 2.2 earthquake struck at 5:37AM GMT approximately 23km from Fleetwood, 25km from Blackpool, 60km from
Liverpool, 74km from Ramsey, 172km from Belfast and 185km from Dublin. A much stronger magnitude 3.2 earthquake struck
the same location at 9:58AM GMT at a depth of 8km, and was felt on the British mainland in Fleetwood, Blackpool and
Thornton-Cleveleys. The larger earthquake was also recorded by INSN seismometers as far away as Donegal and Wexford in
Ireland.
The INSN, which monitors seismic activity in the region, says the magnitude 3.2 earthquake was the strongest quake
recorded in Britain or Ireland since 29th May 2013 when a magnitude 3.8 earthquake struck off the coast of the Llŷn
Peninsula in North Wales.
INSN Director Tom Blake indicated that only residents closest to the epicentre of today’s earthquakes are likely to have felt any shaking. He
added that further tremors were possible during the coming days.
Mr. Blake from the School of Cosmic Physics in the Dublin Institute for Advanced Studies (DIAS) explained: “This part of
the Irish Sea has not seen any significant seismic activity in recent years but ultimately their cause is likely to be
no different than other earthquakes in Britain and Ireland. The last earthquake recorded in this part of the Irish Sea
occurred in 1843 and is estimated to have been a magnitude 4 quake.”
He continued: “Although Britain and Ireland are far from any plate boundaries, much of the Region is still experiencing
quakes due to the removal of the weight of ice sheets that once covered the land. Occasionally this post-glacial
isostatic rebound - the phenomenon of the land surface gradually returning to its pre-glacial contours - results in
earthquakes of this magnitude, particularly in the northern half of the islands.”
Mr. Blake said: “it is impossible to tell if stronger earthquakes will occur in the coming days and weeks, but
aftershocks can be expected even if most if not all will be too weak to be felt.”
Other earthquakes have been recorded in the Irish Sea and along western parts of Britain in the past 6 weeks. They
include quakes at Llanrwst, Conwy in North Wales on July 15th (mag 1.4), Irish Sea off Anglesey on 29th July (mag 1.2),
Islay, Argyll/Bute on 31st July (mag 1.4), Knutsford, Cheshire on 11th August (mag 2.1) and the Isle of Arran on 12th
August (mag 1.3).
The largest known British earthquake occurred near the Dogger Bank in 1931, with a magnitude of 6.1. The largest
earthquake to impact Ireland occurred on the Llŷn peninsula on 19 July 1984. The 5.4 magnitude earthquake was the
largest ever recorded earthquake on mainland Britain and was felt throughout Ireland's east coast, Wales and England.
Aftershocks from the quake measured up to 4.3 on the Richter scale and some structural damage resulted along the east
coast of Ireland.
A magnitude 2.7 earthquake was recorded off the northwest coast of Ireland on November 21st 2012. On June 6th 2012, a
magnitude 4.0 earthquake was recorded off the coast of County Mayo, close to the Corrib gas field. The quake happened
at 9am, 60km west of Aughleam near Belmullet. The most significant land earthquake to be recorded in Ireland in recent
years occurred when a 2.7 quake hit Lisdoonvarna in County Clare in May 2010. It also was the first earthquake to be
recorded in the west of Ireland in modern times.
The DIAS began modern seismic recordings in 1978. The INSN now features 6 permanent stations. 2013 marks 20 years since
the beginning of digital seismic recording of the INSN. For more see www.dias.ie.
ENDS