The first earthquake was recorded at 5:37 am on Sunday, August 25, 2013 and reached a magnitude of 2.4 on the Richter Scale and measured about a mile deep. The second was recorded at the same spot at 9:58am and reached a magnitude of 3.2 and was about four miles deep.
The INSN, which monitors seismic activity in the area, says that the quakes were caused by a process called glacial rebound. During glacial rebound the stress that built up during the weight of glaciers during the Ice Age is slowly released.
Tom Blake, who is the INSN Director and works at the School of Cosmic Physics in the Dublin Institute for Advanced Studies explained to UTV, “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.” He continued, “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.”
Blake also said, “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.”
Fracking tests, which pump a mixture of water and chemicals into the ground to crack sedimentary rock to extract oils, have previously been blamed for tremors in the Lancashire area. The results of a study by Durham University experts in April found that fracking operations were “not significant” in causing earthquakes.
The second quake was the strongest quake recorded in Ireland or Britain since May 29, 2013 when a 3.8 quake struck North Wales. The two earthquakes were recorded 15 miles off the Lancashire coast, which is about 114 miles from Dublin. People in Dublin, Wexford, Wicklow, and Kildare said they felt tremors. The second, larger earthquake was recorded on INSN seismometers in Donegal and Wexford.
More tremors are possible in the coming days, but will likely be too small to feel. 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.”
The largest earthquake to impact Ireland occurred on July 19, 1984 on the Llyn Peninsula. It was the largest earthquake to hit mainland Britain hitting a 5.4 magnitude and it was felt on Ireland’s east coast, Wales, and England. The quakes’ aftershocks reached a 4.3 on the Richter scale and there was some structural damage along the east coast of Ireland.