Mayo earthquake surprises geologists


A LEADING seismologist has said yesterday’s earthquake off the west coast was “unexpected” and poses “very interesting questions for geologists”.

The earthquake, which registered a magnitude of four on the Richter scale, was recorded as 60km west of Belmullet, Co Mayo, at a depth of 3km, at 8.58am. It was the largest local seismic event ever recorded, according to Tom Blake of the Irish National Seismic Network (INSN) and the Dublin Institute of Advanced Studies.

It was also the second-largest local earthquake on record in either Britain or Ireland, he said – the first being of 5.4 magnitude on July 19th, 1984, off the west coast of Wales and felt in Waterford and Wicklow.

A 2.7 magnitude tremor was recorded in Lisdoonvarna, Co Clare, in May 2010.

The Irish Coast Guard recorded instances of structural damage to houses in Erris, Co Mayo, yesterday and the British Geological Survey said the impact was felt in Galway, Mayo and Sligo.

The Geological Survey of Ireland said earthquakes of this magnitude at this depth were “not very unusual although not common”.

However, Mr Blake said that while the earthquake was classified as “moderate”, it was “significant” in that it challenged existing information about seismic activity off the west coast.

The location, just 23km south to southeast of the Corrib gas wells, prompted a call by Sinn Féin councillor for Mayo Rose Conway-Walsh for reassurance that this was not connected to seismic testing Shell EP Ireland was due to initiate on the Corrib gas field last Friday.

She also said many concerned residents wanted to know whether the existing Corrib gas infrastructure had been damaged.

North Mayo hostel owner Betty Schult said the earthquake had shaken the foundations of her 250-year-old stone cottage and she was concerned about the impact on the offshore pipeline for the Corrib gas project and the refinery, situated on bog.

Mr Blake said he had examined the seismic traces and they were “caused by earthquakes and nothing else”.

Shell EP Ireland said the seismic survey had not started and it had “no reason to believe that this event has had any impact on the sub-sea infrastructure”.

“However, as a precautionary measure, a visual inspection of the offshore infrastructure will be carried out in the coming days,” it said.

Phil O’Hara of Aclare, Co Sligo, reported a chunk of her chimney on the ground, while in Westport, Co Mayo, Lorella Errani said she was reading about the earthquake near her mother’s home in Ravenna, Italy, when she heard a “deep rumbling noise”.

The seismic activity was tracked in the Cliffs of Moher visitor centre in Co Clare and on the INSN network of permanent recorders.

The tremors had caused “no unusual wave activity”, said Irish Coast Guard officer Ray Malanaphy. The Coast Guard said it had confirmed this with two vessels working on the Corrib gas field.

Dr Brian McConnell of the Geological Survey said there could be some small aftershocks.