Expert comment on the earthquake in North Yorkshire
(4 January 2011)
Following the earthquake which struck north-west of Ripon in North Yorkshire, England, a Durham University expert has commented on recent seismic activity in northern England.
In December, an earthquake was also felt in locations across Cumbria, Lancashire, south-west Scotland, Yorkshire, Northumberland and the Isle of Man.
Prof Robert Holdsworth, Head of Department, Earth Sciences, Durham University said:
"There is nothing particularly unusual about the occurrence of the two small earthquakes in Northern England, which happened over the Christmas period. The Ripon earthquake was a magnitude 3.6 event and occurred at approximately 6.5km depth, whilst a magnitude 3.5 event occurred in the Coniston area on December 21st 2010.
"By global standards, the UK is not particularly prone to earthquakes, but it does experience between 20-30 events every year that are sufficiently large to be felt by people. Very few of these cause significant damage, though they often make a significant and long-lasting impression on people who experience them."
Q and A: Prof Robert Holdsworth, Head of Department, Earth Sciences, Durham University
1. Are earthquakes in Yorkshire and north-west England rare events?
Larger earthquakes of magnitude 5 and above are very rare, with the largest recent event in the region being a magnitude 4.7 event that occurred in the Carlisle area in December 1979. Yorkshire and NW England have experienced a number of magnitude 3 earthquakes over the last few years, and there are many smaller earthquakes every year, but these are generally not felt by most human beings.
2. What is the cause of earthquakes in the UK?
Earthquakes occur due to slip along geological faults and the release of accumulated stress in the Earth's crust at depth. The cause of earthquakes in the UK is somewhat uncertain. Earthquakes here are likely to be related in part to stresses produced by plate tectonics, but the UK lies well away from currently active plate margins. This is a major reason why there are so few large earthquakes in the UK.
Interestingly, seismicity in the UK may also be triggered by the release of stresses related to the long-lived ‘unloading effect' following the melting of the ice sheets in Northern Britain. This would certainly explain why a majority of earthquakes are located in Wales, NW England and western Scotland.
3. Can we predict earthquakes?
It is very difficult to predict earthquakes with any precision. We do know that bigger magnitude events occur less frequently than smaller events. Thus a magnitude 4 event will occur roughly every 2 years whilst a magnitude 5 event will occur every decade or two.
The crustal rocks beneath the British Isles carry a huge number of old, potentially seismogenic (earthquake-prone) geological faults - a legacy of its turbulent geological past - and there are so many that it is virtually impossible to say where the next event will occur. But one thing is certain: there will be future earthquakes and if you experience one, it will likely be a memorable event in your life!