|Oklahoma earthquakes through Sept. 24, 2016 (USGS graphic)|
"Oklahoma's earthquake swarms have been linked by scientists and state officials to deep injection of drilling wastewater by oil and gas companies," Soraghan writes. "The reduction in quakes has followed a reduction in wastewater injection because of government restrictions and an oil price slump." Prior to the oil and gas boom that began in 2009, Oklahoma averaged only two earthquakes of magnitude 3.0 or higher per year.
"In the past few years, oil and gas regulators at the Oklahoma Corporation Commission have directed about 700 disposal wells in the state to close or scale back operations," Soraghan writes. "Because of that, the amount of wastewater being injected deep underground every day has dropped by about 800,000 barrels, or 34 million gallons. But companies struggling with the oil price slump cut injection by at least another 500,000 barrels a day beyond the state's directives. If prices rise, they could increase that much without violating the directives."