NW hit by two more quakes

The tremors last Tuesday (March 13) and Wednesday (March 14) followed a 2.2 magnitude event in January when several Buncrana residents reported feeling the earth tremble. The quakes were all at depths of between two and three kilometres.

The North West - alongside Wexford - has the highes level of seismic activity on the island with Donegal and Londonderry both lying on a major fault that also runs through Scotland and experiences stress readjustments which are mainfest by - usually - low level earthquakes.

Before the recent Buncrana quakes the British Geology Survey (BSG) had recorded a sequence of at least nine small earthquakes in February on the island of Islay which lies just over 50 miles from Londonderry on the west coast of Scotland.

The largest of the earthquakes had a magnitude of 2.8, while two others had magnitudes in excess of 2. Eight of the earthquakes were felt by local residents who reported that “ the house trembled from side to side,” the “tin sheeted roof shook” and that it felt like “a very large heavy track moving vehicle.”

Whilst the recent “swarm” of activity is relatively low level the BSG says “a number of magnitude 3 plus events have occurred in recent times including a magnitude 3.4 earthquake off Jura in 1998.”

Equally, “larger events have occurred elsewhere in Argyll in recent times including a magnitude 4.1 earthquake near Oban in 1986. The largest known Scottish earthquake occurred nead Loch Awe in 1880, with a magnitude of 5.2.

In a recent report examining the risk earthquakes pose in this part of the world the BSG warned: “One might think that this is not an issue in countries like the UK, but although the scale of the problem is far smaller, similar issues arise.

“Most people have no idea of the earthquake history of their country, and have no knowledge of past earthquakes beyond the scope of living memory. And the same issue of increased exposure to earthquakes applies just as much to Britain as to the rest of the world.

“One of the strongest earthquakes to have affected Britain occurred on 6 April 1580; the magnitude, estimated from the size of the area shaken, was about 5.5, and the epicentre was in the Dover Straits. Although it was some distance away, London was quite strongly affected, probably because the soft Thames clays are more susceptible to being shaken. Nor was this an isolated event; a very similar earthquake occurred in 1382, which also caused damage in London.

“What has happened twice can happen a third time; what will be the effects on the London of today? In 1580, two people in London were killed.

“Modern London has about 40 times as many people living in it and while a comparable earthquake would certainly not cause a disaster on an international scale, the level of shaking would come as an unpleasant shock in a country that tends to think of itself as immune from earthquakes.”

And if until now you thought Britain and Ireland were immune from damaging earthquakes you may be surprised to learn that the British Isles are also at risk of being struck by tidal waves triggered by tremors or landslides elsewhere in the Atlantic.

According to the Geological Survey of Ireland “while tsunamis are low-probability events and very unlikely to be on the scale of the Japanese tsunami, the Irish coast is at risk from tsunamis.”

“Tsunami threats to Ireland include: a repeat of the 1755 magnitude 8.6 Lisbon earthquake, which GSI-commissioned modelling predicts could generate waves up to 4m high on the southern Irish coastline; submarine landslides, such as that which occurred off the Atlantic coast of Canada in 1929 and generated a tsunami that claimed 30 lives in Newfoundland; ancient submarine landslides have been mapped on the Irish continental shelf by the INFOMAR programme that would probably have generated tsunamis; earthquakes along the convergent plate margins in the Caribbean, such as the January 2010 Haiti earthquake which generated local tsunamis; larger tsunamis have been produced in historical times and in future could traverse the Atlantic to affect Ireland; a future eruption of Cumbre Viejà volcano on La Palma, Canary Islands, which might cause a major coastal landslide and trigger a major tsunami that would impact on both European and North American coastlines,” the GSI states.