Earthquakes down 31% in Oklahoma in 2016, but total strength of seismic energy release on the rise

Oklahoma earthquakes through Sept. 24, 2016 (USGS graphic)

The Oklahoma Geological Survey recorded 623 earthquakes of magnitude 3 or higher in 2016, Mike Soraghan reports for Energywire. While that's down 31 percent from the 2015 record total of 903, "some of the quakes were much stronger than in 2015, so 2016 still set a state record for seismic energy release, a measure of strength." In comparison, two of the nation's leading states for earthquakes, California and Nevada, combined for less than 300 in 2016.

"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."