Tuesday, June 18, 2013

Enigmatic earthquake off the North Wales coast

The British Isles are not noted for seismicity, being safely ensconced in the middle of the European plate, which starts at the mid Atlantic spreading ridge where the plates are being pushed apart by upwelling magma. We do have the occasional quake though, and one struck early this morning 8km beneath the Irish sea, 14Km offshore from the coastal town of Abersoch. Measuring 3.8 on the Richter scale, it was felt as far away as Liverpool and Dublin.

This area of the Irish sea is more seismic than average for the UK, and scientists are puzzled as to why, since there has been an increase in activity these last few months along the whole west coast of Britain. The Llyn peninsula, closest to the epicentre was the location of Britain's largest onshore quake in 1984, when buildings were damaged by a 5.4 magnitude tremor, swiftly followed by two magnitude 4 shocks. There are no obvious plate boundary faults to produce these quakes, and possible explanations range from the reactivation of an old lineament (line of weakness), through tectonic push forces from the spreading ridge to isostatic rebound (the land bouncing back up after the melting of the ice age glaciers removed the pressure from the weight of the ice). Weak aftershocks are expected, but scientists are not predicting any significant increase in activity.

Here on TES we often report the large and spectacular events from around the globe, but the small and enigmatic ones are those that prompt scientists to ask the sort of questions that lead to new insights. As the famous quote goes, the best science starts with the words 'That's funny' rather than Eureka.

We did a past post on tsunami risks to Atlantic Ocean coastlines, available at http://tinyurl.com/q5l47mb.

Image credit: David Medcalf

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