UK experiences three earthquakes a year due to human activity, study says

At least three earthquakes strike the UK every year as the result of human activity, according to a new study.

Most of the tremors in recent decades resulted from coal mining, but fracking exploration caused two small earthquakes in 2011. The new work is the first in the world to set a national baseline and will allow the detection of any rise in earthquakes that follows an expansion of UK shale gas exploration in the future.

“Understanding what the current situation is imperative, otherwise how can we say with any confidence in the future what the impact of fracking has been nationwide?” said Professor Richard Davies, at Newcastle University, who led the research which is published in the journal Marine and Petroleum Geology.

Earthquakes caused by collapsing mines or fracking are usually small, with many going unnoticed by people. But the largest ones can cause anxiety for local people and damage to fragile structures.

“Historically, fracking-related earthquakes have been small, but the UK is criss-crossed by faults – some of which may be critically stressed – and if triggered these could result in earthquakes that people can feel,” said Professor Davies.

Man-made earthquakes have been known in the UK since at least 1755, when collpasing lead mines in Derbyshire shook the ground. The research team analysed the 8,000 earthquakes recorded under the UK (excluding surrounding sea) between 1970 and 2012.

In the past, earthquakes linked to human activities were more common in the UK, with over 40 recorded in 1991. But as the nation’s deep coal mines closed, the number of tremors has fallen by 95%.

Since 1970, at least one in five earthquakes under the UK have been man-made, according to the new analysis. The true number may be higher, as many tremors could not be classified as natural or man-made due to a lack of information. If half of the unclassified earthquakes were in fact caused by human activities, the average number of man-made tremors rises from three to 12 every year.

While seismicity has fallen in recent decades, the UK government’s determination to push ahead with shale gas exploration has raised the prospect of it increasing once again. In 2011, Cuadrilla’s exploration at Preese Hall in Lancashire, led to a 2.3 magnitude earthquake, followed two months later by a second earthquake. Fracking was then suspended until new regulations were implemented to limit the risk of earthquakes.

“Worldwide, the biggest published example of a fracking earthquake to date is 4.4 in magnitude, recorded in Canada in 2014, although an event of this size in the UK is highly unlikely,” said Prof Davies.

Experts believe man-made earthquakes in the UK’s shale-bearing rocks are unlikely to be greater than magnitude 3, which rarely cause any damage. Tremors under magnitude 2 are frequently not felt by people on the ground.