Belfast Telegraph

Monday 15 September 2014

Earthquake: From 8km deep in the earth beneath north Wales came a rumbling that shook Banbridge and rattled the Antrim Glens

BY CHRIS KILPATRICK

The epicentre of the earthquake in the Irish Sea was 15km away from the town of Abersoch, in Wales
The epicentre of the earthquake in the Irish Sea was 15km away from the town of Abersoch, in Wales
This image, reproduced by permission of the British Geological Survey shows the seismogram
 of a level 3.8 magnitude earthquake, that hit close to North Wales, that was felt over an an area of 140km by people who reported "intense shaking". PRESS ASSOCIATION Photo. Issue date: Wednesday May 29, 2013. See PA story QUAKE IrishSea. Photo credit should read: British Geological Survey/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.
This image, reproduced by permission of the British Geological Survey, shows the seismogram of the North Wales earthquake
This image, reproduced by permission of the British Geological Survey shows the location where a 3.8 magnitude earthquake, close to North Wales hit, that was felt over an an area of 140km by people who reported "intense shaking". PRESS ASSOCIATION Photo. Issue date: Wednesday May 29, 2013. See PA story QUAKE IrishSea. Photo credit should read: British Geological Survey/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.
This image, reproduced by permission of the British Geological Survey, shows the location of the earthquake off the Welsh coast

The shaking was felt from Cushendall to Donegal. Ireland is not renowned for its earthquakes, but yesterday our island home was jolted by significant seismic shifts emanating from several miles below the Earth’s surface.

But rather than diving for cover under kitchen tables and crouching under stairs, the chances are that most of us slept through the 3.8 magnitude quake.

Residents in Craigavon and Banbridge reported feeling tremors when it struck in the early hours of yesterday. It was also picked up by a seismic reader in Cushendall.

The tremor centred on the Lleyn Peninsula in Gwynedd. The British Geological Survey (BGS) said the centre point was between the Welsh seaside towns of Aberdaron and Nefyn.

It was felt throughout England and Ireland, with people in Dublin describing “intense shaking” at 4.16am.

There were no reports of damage or injury.

“Anybody within 150km-180km of the epicentre would have felt something, a slight vibration,” a spokesman for the BGS said.

“But even the people at the centre just reported some windows rattling.”

The BGS reported receiving more than 100 reports from people who felt the earthquake.

A spokesman said the size of the tremor was not unusual for the UK, adding that Northern Ireland was one of the least affected areas in Europe for seismic activity.

The Irish National Seismic Network (INSN) said further earth tremors are likely in the coming days in the Irish Sea and in north Wales.

The quake was measured at a depth of 8km and was followed four minutes later by a smaller 1.7 magnitude tremor at a shallower depth of 3km.

INSN director Tom Blake, from the School of Cosmic Physics in the Dublin Institute for Advanced Studies, said there has been a significant increase in seismic activity in the area in recent months and that further minor earthquakes are likely. He suggested, however, that the earthquake was moderate enough to have relieved any pressure built up in the region and that it was unlikely to be a precursor to a stronger earthquake.

Mr Blake said: “A 2.3 magnitude earthquake struck this very same area on February 7 and since then there have been a number of other tremors building up to this morning’s event.

“We would ask people in Ireland or Wales who may have felt this morning’s earthquake to submit felt reports to us online at www.dias.ie.”

Dr Brian Baptie, head of seismology at the BGS, said that the size of the tremor was not unusual for the UK.

“We get an earthquake of this size in the UK maybe once or twice every couple of years,” he said. “We also know that north Wales is one of the more seismically active parts of the UK.”

The latest tremor was just a few miles from the point on the Lleyn Peninsula where an earthquake struck in July 1984 with a magnitude of 5.4. — the most powerful recorded in Britain in the past 200 years.

Bob Holdsworth, Professor of Structural Geology at Durham University’s Department of Earth Sciences, said: “Compared to areas of the world located at major plate boundaries such as the west coast of America and the Himalayas, the British Isles are relatively untroubled by major destructive earthquakes.

“Yet there is puzzling and persistent recent history of smaller-scale seismic events, the origins of which remain enigmatic.

“The Llyn Peninsula seems to be a particular hotspot for small to medium-sized earthquakes, a fact that may be related to the presence of a major NE/SW trending ancient fault zone running through the Menai Straits.”

”Strangely, however, it has proved difficult to conclusively prove a direct association between the observed seismicity and reactivation of the many old faults that criss-cross the crust of Britain.

“We need further research to better understand the locations, causes and likely magnitudes of earthquakes in the UK.”

Factfile: why it happened

The British Isles are not located on a fault, such as the volatile San Andreas line in California, which lies on a plate boundary. They are instead positioned “mid-plate” and affected by two different driving forces.

The first is dictated by the Mid-Atlantic Ridge, a point under the ocean between Ireland and America where two plates are slowly pulling apart. The pulling motion causes friction which leads to earth tremors hundreds of miles away. The second factor is the lingering after-effect of the Ice Age, which is still causing the Earth’s crust to ‘bounce’ slightly and very slowly.

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