The number of earthquakes in Oklahoma fell by 52 percent between January and April of this year, according to an Energy In Depth review of data from the Oklahoma Geological Survey. The data also show the number of monthly earthquakes has fallen by 55 percent since a June 2015 peak.

In January 2016, Oklahoma had 172 earthquakes of at least a magnitude 2.8, which is the minimum size for which the OGS has a complete catalog. That was less than the number the state had experienced in June 2015, when 183 perceptible seismic events occurred.

But so far, for every month of 2016, Oklahoma has recorded fewer earthquakes than the preceding month. In April, the state experienced 82 seismic events.

The decline in seismicity comes after numerous steps taken by the Oklahoma Corporation Commission, which regulates the oil and natural gas industry, to reduce disposal volumes in targeted areas and apply greater scrutiny to new injection permits. Many of those measures, called “directives,” have been supported by the industry.

Since last summer, the OCC has implemented more than a dozen directives and other measures in response to earthquake activity. The plans have included increased monitoring, well plugging, and volume reductions for hundreds of injection sites near seismic events.

Jeremy Boak, director of the Oklahoma Geological Survey, told Scientific American in March that he was starting to see declines in earthquake rates in the state, specifically in the areas impacted by the OCC’s directives. He acknowledged, however, that it still may be too early to tell if this is a lasting result.

Michael Teague, Secretary of Energy & Environment in Oklahoma, has also noticed a drop in seismicity. “We are seeing declines in the earthquake activity,” said Teague recently.

Industry Supportive

Despite the “significant economic impact” that some of the OCC’s actions have had on oil and natural gas companies, the industry has generally been supportive of the state’s response.

“With the swarm we’ve had, we think the action the commission is taking is prudent,” said Kim Hatfield with the Oklahoma Independent Petroleum Association last fall, after a series of seismic events around Cushing.

Chad Warmington with the Oklahoma Oil and Gas Association also said earlier this year that the industry “will continue collaborating with state officials, regulators and researchers to determine what information is needed to help make informed, scientific-based decisions that reduce seismic activity in the state.”

The industry has invested over $35 million to reduce earthquake risks since March 2015. Companies have also helped secure funds for additional seismic monitoring stations and shared proprietary data with scientists and regulators, including information on previously unmapped faults.

“The amount of collaboration and cooperation we have had around this issue has been tremendous, like nothing I’ve ever seen,” said Dana Murphy with the Oklahoma Corporation Commission.

Progress, but Work Continues

In March, the OCC expanded its earthquake response plan, including additional monitoring in an area that covers more than 10,000 square miles.

Scientists have said that volume reductions or other mitigation measures may not yield impacts immediately, and could take several months before seismicity declines.

“It is important to note,” the OCC wrote earlier this year, “that researchers agree that any decrease in earthquakes that may result from such plans is rarely immediate, and must be evaluated over the course of several months.”

Coincidentally, seismic levels ticked upward in late December of 2015 and into early January of 2016, although the number of events was still below summer 2015 levels. Since then, felt seismic activity in Oklahoma has declined every month.

As Energy In Depth reported last year, experts have also said that new restrictions could actually lead to an increase in earthquakes, at least in the short term.