A study published in Science explains how wastewater injection sites, areas where toxic water left over from oil drilling and fracking processes is injected into the ground, could be driving a sharp increase in disastrous earthquake events being witnessed in the US.

The toxic water left over from oil drilling and fracking processes is injected between impermeable layers of rocks to avoid polluting freshwater.

More than 230 earthquakes with a magnitude greater than 3.0 have shaken the state of Oklahoma already this year. There have also been well-documented cases of wastewater injection-driven quakes in Ohio, Utah, Colorado and British Columbia within the last year.

Past research has shown that processes such as wastewater injection at oil drilling and fracking sites could induce a small number of earthquakes in the vicinity but scientists have never been able to link some of the more distant or stronger earthquakes with these sometimes faraway wastewater wells. The latest study does that.

"It really is unprecedented to have this many earthquakes over a broad region like this," said study co-author Geoffrey Abers of Cornell University. "Most big sequences of earthquakes that we see are either a main shock and a lot of aftershocks or it might be right at the middle of a volcano in a volcanic system or geothermal system."

The team determined that a relatively small number of wastewater injection sites used in oil drilling and fracking in Oklahoma may have the ability after all to induce relatively strong earthquakes a long distance away, throughout the state. Some of these earthquakes were as much as 20 miles away from what seems to be the primary wells.

Scientists have known since the 1960s that wastewater injection, during which millions of barrels of wastewater is forced into a disposal well, can induce earthquakes by increasing the fluid pressures underground. With shale exploration being the next big fuel rush across the world, fracking has also added to the concerns of environmentalists.

The fracking process involves pumping water, sand and chemicals into rock at high pressure in order to extract the fuel from the shale deposits. Some governments have banned the process.

The UK government has recently proposed new rules to access land in a bid to speed up the introduction of fracking. It proposes that shale oil and gas companies are granted access to land below 300m from the surface.

The consultation comes as a new report by the British Geological Survey (BGS) estimates there are 4.4bn barrels of oil in shale rocks in southern England. Energy Minister Michael Fallon has observed that Britain needs more home-grown energy. "Shale development will bring jobs and business opportunities."

There have been strong anti-fracking protests at Balcombe, West Sussex, against test-drilling.