Oklahoma's earthquakes on the wane after wastewater rules take hold

After a sudden increase in earthquakes, which have been linked to oil extraction practices, Oklahoma instituted new limits on wastewater injection. Since then, the quakes have dropped off significantly, according to a new analysis. 

First Look

The rate of man-made earthquakes in Oklahoma linked to oil fracking practices has dropped significantly since new limitations took place in May, according to an Associated Press analysis of US Geological Survey data.

Earlier this year, before new regulations requiring a 40 percent reduction in injecting wastewater into energy wells went into effect, Oklahoma was experiencing 2.3 quakes of magnitude 3.0 or higher per day, on average. Since then, that average has dropped to 1.3 per day, although several quakes since then have been damaging. Meanwhile, neighboring Kansas has also seen a decrease in quakes after putting limits on wastewater injection.

"Definitely the rate of quakes have gone down," USGS geophysicist Robert Williams told the Associated Press. "At the same time we had more magnitude 5s this year than ever before historically in Oklahoma. It's good news on one hand. It's heading in the right direction, but troubling to see these large damaging quakes in Pawnee and Cushing."

Before 2009, the state averaged just one magnitude 3.0 or higher earthquake a year, before the sudden jump in recent years, which many scientists blame on the injected wastewater. Fracking and other types of oil extraction require a great deal of water, which becomes contaminated. In order to prevent pollution of drinking water, oil extraction companies dispose of the wastewater below ground, where they add more pressure to small fault lines. 

Earlier policies in Oklahoma, instituted in March 2015, were targeted at reducing those stresses, as The Christian Science Monitor reported in August, with a "traffic light system" to monitor seismic activity and inform decisions about wastewater disposal. 

Kansas has seen a similar trend in man-made earthquakes. From 2000 to 2013, Kansas did not have more than four earthquakes of magnitude 2.5 or greater per year. In 2014, however, the state better known for tornadoes saw 154 such earthquakes. However, since putting limits on wastewater injection, the number of earthquakes has begun to drop.

Solutions are not one-size-fits-all, however. Each state's geology is unique, Ryan Hoffman – the director of the Kansas Corporation Commission, the agency that issued the March 2015 order to put a cap on well injections – told the Monitor last January. "Rather than approaching the issue on a statewide or national scale, it is important to identify the areas more susceptible and take whatever actions are necessary for that specific area," he said. 

In Oklahoma, however, quakes are on a trajectory to eventually return to pre-2009 levels, according to a study published Wednesday in the journal Science Advances.

"We're not out of the woods yet. There is still a possibility for potentially damaging earthquakes," Mark Zoback, a Stanford seismologist and the author of the study, told the Associated Press. "It's going to take a few years for the situation to return to normal."

Matt Skinner, a spokesman for the Oklahoma Corporation Commission, which oversees oil and gas operations, agrees that it will take time to return to 2009 levels, but says regulations could put the state on the right path. 

"Obviously the goal is to bring seismicity down to what, for Oklahoma, would be considered a normal level. That's the goal," Mr. Skinner told the Associated Press. "Things will take time, but we're going to move ahead with actions that will hopefully make that time sooner rather than later."

This report includes material from the Associated Press.