Earthquakes rattled central Oklahoma Friday night. Steps taken to minimize risk of more

Numerous earthquakes and aftershocks that struck Oklahoma late Friday into Saturday morning near Prague left rattled nerves, scattered dishes and bric-a-brac, cracked drywall, and some tumbled bricks, but no reported injuries.

"Last night was exciting to say the least. Thankfully so far the reports of injuries have been zero," the Lincoln County Office of Emergency Management posted on Facebook Saturday morning, along with a link to the state site for reporting damage.

Nearly 40 quakes had struck by 11 a.m. Saturday starting with the big one − by Oklahoma standards − at 5.1 magnitude, according to the U.S. Geological Survey, using data provided by the Oklahoma Geological Survey.

The Oklahoma Corporation Commission Oil and Gas Conservation Division ordered oil field wastewater disposal wells in the Arbuckle formation within 10 miles of Prague to begin shutting down operations, as its "initial response to mitigate the risk of further seismic activity," spokesman Matt Skinner said Saturday afternoon.

"The gradual shutdown process is necessary to avoid sudden pressure changes that could result in more seismic activity," Skinner said. "The Arbuckle formation is the state’s deepest formation.

"Oil and gas wastewater disposal into the Arbuckle formation has been linked to seismic activity in parts of the state. It should be stressed that that this action is an initial response. Further study may result in new directives."

Weekend quakes were in the same area as the 2001 quake near Prague, Oklahoma

The first earthquake, across Oklahoma and in neighboring states, was at 11:24 p.m Friday, 5 miles northwest of Prague, about 60 miles east of Oklahoma City, the USGS said. The rest were in the same area between Prague and the tiny Sparks community 15 miles to the northwest.

It was in the same area as the 5.7-magnitude quake in 2011 that led to a lawsuit against two state oil and natural gas companies over property damage, which was settled in 2017. Settlement of a second lawsuit from the 2011 Prague quake was announced just last fall.

The lawsuits that the 2011 quake was caused by oil and natural gas drilling companies' wastewater disposal wells.

Prague earthquakes probably tied to drilling wastewater disposal

State seismologist Jake Walter said Saturday that this weekend's quakes also are probably related to disposal wells, which inject waste fluid into porous geologic formations underground. The Oklahoma Corporation Commission said Saturday that it was investigating.

Walter noted that there was no indication that "fracking" caused the quakes.

Drilling companies use hydraulic fracturing in production. Underground or ground water is mixed with additives to make fracturing fluids, which are then injected into targeted rock formations to free crude oil. However wastewater disposal comes at the end of the fracturing progress, according to the Environmental Protection Agency.

Oklahomans: Brace for more earthquakes, state seismologist says

People in the Prague area can expect more, Walter said Saturday in a statement from the Oklahoma Geological Survey.

"We should expect several strong aftershocks in the coming weeks that may be widely felt," he said. "Whereas most aftershocks are smaller than the main shock, a very small fraction of aftershocks result in a larger earthquake than the main event. The seismic hazard remains high in the area."

People should secure valuables that might shake during strong aftershocks and be ready Drop, Cover, and Hold On.

Walter added, "The event occurred in nearly the same area as the 2011 (magnitude) 5.7 Prague earthquake that has been identified as having been induced by wastewater disposal activities. We will continue to monitor the seismicity and provide assistance to the Oklahoma Corporation Commission, other state agencies, and the public."

Social media reactions to weekend Oklahoma earthquakes

People in Norman, Oklahoma City, Shawnee, Tulsa, Bartlesville, southeast Kansas and north Texas quickly took to social media to report the shaking.

Barbara Vice, in Tulsa, said on Facebook that she and her cat, Ham, stirred during the first quake, but that she didn't realize the extent of it until she saw social media Saturday morning. She is semi-retired as owner, publisher and editor of the Drumright Gusher and later, the Yale News.

"I’d been asleep maybe 15 minutes when I was half awakened by what I thought was my 22 lb. cat jumping off the bed and spazzing around the room for a bit," she posted. "But I never fully woke up and so had no idea what happened until I saw everyone’s posts this morning.

"My guy’s daughter had pics fall off the wall at her house … all the way over in Tahlequah! It’s crazy how far the shaking can travel. It sure reminds us of just how very tiny we humans are."

Earthquakes

Friday's temblor came just a few weeks after a cluster of earthquakes were reported near Arcadia. The largest of those earthquakes was a 4.3 magnitude.

This is a developing story.

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This article originally appeared on Oklahoman: A preliminary 5.1 magnitude earthquake struck in central Oklahoma Friday