Fracking a cause of earthquakes?

THE US state of Oklahoma is investigating whether a more than 20-fold jump in the number of earthquakes in the past two years is connected to a surge in fracking, the controversial drilling method used to extract shale gas, The Independent has learnt.

The number of earthquakes recorded in the state soared from its historical average of about 50 a year to 1,047 last year and is likely to match or break that this year, said Austin Holland, a seismologist at the Oklahoma Geological Survey.

Mr Holland made his prediction in the aftermath of some of the strongest earthquakes the state has seen over the weekend, continuing a spate of seismic activity which scientists are struggling to understand. Until last year, the highest number of earthquakes Oklahoma state had recorded was 150, in the mid-1990s.

The practice of fracking, or hydraulic fracturing, involves pumping water, sand and chemicals at high pressure into shale rock, to release the gas it holds.

Mr Holland estimates that the volume of shale gas extraction in Oklahoma has "roughly doubled in the past few years". There are currently tens of thousands of so-called fracturing wells in operation.

"It is certainly possible for fluid injection to cause earthquakes, so we know it's possible, it's just we don't know how often," Mr Holland said.

"This is an important issue for the state, the nation and the globe."