Did the earth move for you thirteen years ago exactly, on the morning of July 19th, 1984? If by chance you were near the east coast of Ireland at the time, perhaps it did, because at 6.56 am that day there was a minor earthquake. The tremor had its epicentre in the Irish Sea just west of Anglesea, and a magnitude of 5 or thereabouts on the famous Richter scale. It was noticeable in Dublin, for example, as a rumbling sound and as a very palpable vibration.
We tend to think of earthquakes as being nasty foreign things to which we in these parts are immune. And of course, severe tremors are normally confined to parts of the world lying near the interfaces between the major "plates" that make up the surface of the Earth. But minor tremors may occur virtually anywhere in the world. They are usually associated with faults, or discontinuities, in the rock strata of the Earth's crust, often originating deep below the surface, and as we have seen, they happen here in Ireland now and then.
There was a gentle tremor of 2.1 on the Richter scale, for example, on November 21st, 1994, in Donegal, and a similar event in Midleton in Co Cork in 1981. Some experts believe that some 5,000 years ago earthquakes hitting 6 or 7 were not unknown in Ireland, perhaps associated with an elastic resurgence of crustal layers relieved at last of the considerable weight of the recently retreated glacial ice.
By and large, however, in historical times, Ireland has been seismically rather uneventful, 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 stones falling from the nearby Christ Church. The greatest earthquake in Britain in recent years was centred near Colchester in Essex, and occurred at 9.18 am 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.