Twice every minute an earthquake strikes

 

Throughout the world there are about one million earthquakes every year; an average, if you work it out, of a little under two per minute. The vast majority are very light and hardly noticeable; about 20 might be categorised as "serious"; and about five on average result in loss of life or cause significant damage.

The United States has about 700 every year that make the news, and Britain and Ireland have an average of two or three of any severity that merit mention in the papers.

Perhaps the most newsworthy tremor ever felt in Ireland was that which occurred 16 years ago today, on the morning of July 19th, 1984. It happened at 6.56 a.m., with its epicentre in the Irish Sea just west of Anglesey, and had a magnitude of five or thereabouts on the Richter scale. It was noticeable along large sections of the east coast, particularly Dublin, as a rumbling sound and as a very palpable vibration.

Others have occurred from time to time. Ten years later, for example, there was a gentle tremor of 2.1 on the Richter scale on November 21st, 1994, in Donegal. And earlier, there was a similar event in Midleton, Co Cork, in 1981.

Experts believe that some 5,000 years ago earthquakes of magnitude six or seven were not unknown in Ireland, perhaps associated with an elastic resurgence of crustal layers relieved of the considerable weight of the then recently retreated glacial ice.

By and large, however, Ireland has been seismically uneventful in historical terms, and we must look to our neighbouring island for the real action. On June 1st, 1246, for instance, it is recorded that "there happened so great an earthquake in England that the like had seldom been seen or heard. In Kent it was more violent than in other parts of the Kingdom, where it overturned several churches".

Then in April 1580, in the same area, "three distinct shocks were felt, so that at Dover, part of the `white cliffs' fell into the sea, carrying away a portion of the castle wall". The same tremors caused masonry to fall from the eaves of St Paul's Cathedral in London, and an apprentice was killed by falling stones from the nearby Christ Church. The event still retains the unenviable distinction of being the only known fatality by earthquakes on these islands.

The greatest earthquake in Britain in more recent times was centred near Colchester in Essex, and occurred at 9.18 a.m. on April 22nd, 1884; many chimney stacks were thrown down, and within a radius of seven miles of the town more than 1,200 buildings had to be repaired.