A fifth of earthquakes recorded in UK from 1970 to 2012 caused by human activities: Study

The UK experienced one in five earthquakes that were man-made  every year, reveals a study which could provide a baseline for future impacts of fracking.

Researchers studied 1,769 seismic events between 1970 and 2012 of 1.5 magnitude and higher, the minimum detectable threshold – which suggested that at least a fifth (21 per cent) were caused by human activities, mostly coal mining.

Since the 1980s though, there had been a sharp decline in the number of earthquakes. The 1980s was the time when the coal industry collapsed.

According to the study published in the journal Marine and Petroleum Geology, since 1999, human activities had resulted in on average at least three onshore earthquakes each year of magnitude 1.5 or above which could often be felt.

These included two tremors due to fracking in Lancashire in 2011 before the imposition of a temporary ban on the practice.

According to professor Richard Davies of Newcastle University, who led the research, it provided the world's first baseline for the impacts of fracking, or hydraulic fracturing in the UK, before exploitation of shale gas through the process was ramped up.

The government had said it was going "all out for shale" for boosting energy security and the economy however opponents feared fracking - in which liquid is pumped deep underground at high pressure to fracture rock and release gas - caused earthquakes and other environmental problems.

''Understanding what the current situation is, is imperative, otherwise how can we say with any confidence in the future what the impact of fracking has been nationwide?'' Davies said.

Earthquakes resulting from collapsing mines or fracking were usually small, with many going unnoticed by people, though the largest ones could cause anxiety to locals and damage 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 Davies.

''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 Davies.

According to experts man-made earthquakes in the UK's shale-bearing rocks were unlikely to be greater than magnitude 3, which rarely caused any damage. Tremors under magnitude 2 were frequently not felt by people on the ground.