A spike in earthquakes across Oklahoma is forcing the state's energy regulator to urgently consider tougher restrictions on drilling activity. From June 17 to 24, there have been 35 earthquakes of magnitude 3.0 or greater in the state, according to the Oklahoma Geological Survey. Particularly worrying for regulators, some of the recent quakes occurred in the Oklahoma City metropolitan area, where there are no high-volume wastewater injection wells.
The spike in quakes comes roughly two months after new rules governing the disposal of briny wastewater from drilling took full effect. Drillers were ordered by the Oklahoma Corporation Commission (OCC), which regulates the oil and gas industry, to stop disposing wastewater below the state's deepest rock formation, believed to be one of the main causes of the quakes, and to reduce the depth of wells that already go that deep.
"We have to approach it anew," said Matt Skinner, a spokesman for the OCC. "There's been a huge increase. That's a game-changer," he said, referring to the recent jump in tremors. Oklahoma has been grappling with a rise in seismic activity since 2009, amid an expansion of drilling activity that has doubled the state's oil output in the last seven years. The energy boom has created jobs and contributed to state coffers, but many residents are deeply uneasy about the tremors.
Related: Fast-Track Fracking: Study Says Bigger Injections Trigger More Quakes
It was not immediately clear why there was a spike in quakes in the last eight days. Prior to this period, quakes of magnitude 3.0 or greater typically hit Oklahoma once or twice a day, according to data from the U.S. Geological Survey. Prior to 2009, there were only one or two such quakes in the state in a year.
Related: EPA Says Fracking Has No 'Widespread' Impact on Drinking Water
Scientists attribute the general rise in tremors to soaring amounts of salty wastewater being injected underground. Injected liquid volumes have doubled from about 80 million barrels per month in 1997 to about 160 million barrels per month in 2013, according to a study by Stanford researchers published this month. The drilling boom is due in part to the expanded use of hydraulic fracturing, or "fracking," to access oil and gas in tight shale formations, although the salty wastewater being injected into Oklahoma's disposal wells is found naturally in formations along with the oil and gas, and are not fracking fluids.