In the five years since earthquakes first began blitzing Oklahoma, state officials have been hesitant to agree with scientists who blamed the oil and gas industry.
The shaking doesn't appear to be slowing, but the regulatory response is ramping up as more state officials acknowledge the link between increased seismic activity and waste fluid pumped into the disposal wells of oil fields.
To show how an oil and gas boom fueled a massive surge of earthquakes, scientists used algorithms, statistics and computer models of fluid flow and seismic energy.
But all that is useless without a pickup truck that can handle the dirty back roads of the Oklahoma oil patch.
North of Oklahoma City, Gary Matli inspects a bunch of disposal wells. Matli is with the Oklahoma Corporation Commission, which oversees the oil and gas industry. He's like an oil-field hall monitor — if the industry breaks the rules, he turns its names in.
"You pull onto a well and check the gauges," he says. "There usually are three gauges on the well. One on the tubing, one on the casing and one on the surface casing."
"They want to monitor these to see what possibilities these have of maybe being part of some of this — these seismic events that have been going on."
Economically, the oil industry is everything in Oklahoma.
When Gov. Mary Fallin mentioned earthquakes at last year's state energy conference, she was skeptical. "We all know about the recent seismic activity," she said. "Many have been quick out in the public sector, or even in the private sector, to draw conclusions about its cause."
As scientific evidence mounted, politicians and government officials changed their tune. Speaking at the state Capitol last month, Fallin for the first time publicly agreed with what researchers have said for years.
"I think we all know now that there is a direct correlation between the increase of earthquakes that we've seen in Oklahoma [and] disposal wells," Fallin said.
Disposal wells are the sewers of the oil field. Oil and gas companies pump them full of waste fluid from drilling and fracking. That fluid can cause stressed faults to slip and trigger earthquakes.
Oklahoma's recent oil boom was followed by a surge of earthquakes. Last year set the record with more than 5,000 earthquakes. This year, so far, there have been more than 4,000.
Back in the oil field, the inspections come back clear. The oil companies are complying with the earthquake-related cutbacks the agency recently ordered.
The commission's Matt Skinner steers his pickup down a rutted road as he heads to the next site. "Up until relatively recently, this was the most seismically active area we had in terms of magnitude and number of quakes," he says.
As Oklahoma politicians and public officials have come to terms with oil- and gas-extraction-triggered earthquakes, the regulatory response has quickened.
These days, authorities are more likely to shut down a disposal well or slash how much and how fast the industry pumps fluid underground.
Still, it could take a long time to know whether this has any effect.
"Every day that goes by without a serious seismic event in this area is good news," Skinner says.
There's optimism in the Oklahoma oil patch. There hasn't been a 4.0 or greater quake in this area since volume cuts were ordered and other wells were shut down.
Joe Wertz reported this story for NPR's StateImpact Oklahoma.
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