The third-largest earthquake in recorded state history rocked parts of western Oklahoma on Saturday morning near the site of other large, recent temblors.
The quake registered a magnitude of 5.1 and was recorded northwest of Fairview at 11:07 a.m., according to preliminary estimates from the U.S. Geological Survey.
A 3.9 aftershock followed about 10 minutes after the earthquake, according to the USGS.
At 5.1, the temblor will be the state’s third-largest earthquake, according to Oklahoma Geological Survey data.
The state’s largest earthquake is a 5.6 recorded out of Prague in 2011. The second was a 5.5 recorded near El Reno in 1952. Before Saturday, those two were the only quakes in state history to exceed a 5.0 magnitude.
Saturday’s quake surpassed a 4.8 recorded on Jan. 6 for this year’s largest earthquake. Both the 4.8 and Saturday’s 5.1 were centered near Fairview, according to USGS data.
Officials were preparing a further response to the state’s earthquake outbreak even before Saturday’s temblors.
The Oil and Gas Conservation Division of the Oklahoma Corporation Commission on Tuesday is scheduled to release details of a large regional plan to address the continuing earthquakes in such areas as Fairview, Cherokee, Medford and elsewhere in the western region, according to a release from the commission.
“We have long been worried about the earthquakes in that area, in the sharp rise in seismicity,” OCC spokesman Matt Skinner said. “Obviously, ... it takes time to put together the plan.”
The plan involves a large-scale regional reduction in oil and gas wastewater disposal for an approximately 5,000-square-mile area in western Oklahoma and will affect more than 200 Arbuckle disposal wells, the release states.
“In this case, there is nothing more to be done — we have a plan in place to deal with this,” Skinner said. “To be clear, we’ll release the specific details on Tuesday publicly, but the plan itself is already in place and the operators started to be notified on Thursday of this week.”
How the commission has responded to seismic events has evolved over the years. Two years ago, for example, commissioners took a well-by-well approach, Skinner said.
“As the data becomes available to the researchers we’re working with, we’re putting together these plans, and these plans will continue until we obviously have brought the overall rate down,” he said. “As the knowledge grows, so will the plan.”
Researchers agree that disposal wells injecting into the Arbuckle formation pose the highest potential risk for causing damaging earthquakes in Oklahoma.
The action taken by the commission is not a response to Saturday’s event specifically, but to the overall increase in earthquakes in the region, Skinner said.
The whole region is the newest area of production and has been steadily growing.
“This latest event simply underscores — it’s like the big bold underline — how important it is to put this plan in place,” Skinner said.
Before Saturday, Oklahoma had been shaken by seven earthquakes of at least 4.0 magnitude in 2016. Those quakes were all recorded within the first eight days of January.
The strongest of those — the 4.8 on Jan. 6 — was among a swarm of 32 earthquakes recorded over a period of about 24 hours.
Through Friday evening, Oklahoma had recorded 133 quakes this year that measured at least 3.0, according to the Oklahoma Geological Survey.
As of Saturday evening, the USGS had recorded more than a dozen earthquakes with a magnitude of 2.5 or greater in Oklahoma, including the magnitude-5.1 temblor. All but three were in the Fairview area.