Oklahoma has been hit with a "swarm" of more than 70 earthquakes in the past week, part of the spike in seismic activity thought to be linked to wastewater disposal, according to reports.
The largest quake, which hit on Wednesday near the northern town of Fairview, had a magnitude of 4.8 and was widely felt throughout the state. It was one of two quakes that occurred just 30 seconds apart. The other measured 4.7, according to reports.
They were the largest temblors the state has seen in years, and came less than two weeks after a 4.3 quake was felt in an Oklahoma City suburb.
The state has seen an explosion in earthquakes since the boom in hydraulic fracturing.In April, the Oklahoma Geological Survey linked the the state's 600-fold seismicity rate increase to wastewater injection.
The Oklahoma Corporation Commission, the state's chief oil and gas regulator, has so far called for operators to shut down or reduce volumes at more than 500 wells this year in an attempt to mitigate the impact of water injection on seismic activity.
But such moves are coming under greater scrutiny by legislators and operators alike. State Representative Cory Williams told local outlet The Oklahoman that he was tired of the commission's "reactive" approach.
"We are so reactive that we will wait for the big one. Once we have real loss of property — not a chimney falling off — or God forbid, loss of life, then we'll act. But I don't see the political will there. It baffles me," the Oklahoman quoted Williams as saying.
Another representative has called for a moratorium on disposal wells near earthquake activity.
Meanwhile, the commission has seen some pushback from the industry as well. US independent Sandridge Energy has refused to comply with the commission's voluntary orders to shut-in certain wells because doing so could have a "material adverse effect" on Sandridge's business as a whole, the company has said.
The commission is expected to file legal action against Sandridge soon.