Update: A new 24-hour period has started, and five more Oklahoma earthquakes have been recorded. The latest are a 3.7 magnitude quake near Alva at 8:01 a.m. Friday, a 4.1 magnitude quake near Fairview at 7:36 a.m., a 2.7 magnitude quake near Medford at 3:54 a.m., a 3.4-magnitude quake near Medford at 11:37 p.m. Thursday and a 2.7-magnitude quake near Pawnee at 11:49 p.m.
A rash of 32 earthquakes that shook the state Wednesday night and Thursday increases the likelihood that Oklahoma will experience a higher-magnitude quake, Jeremy Boak, director of the Oklahoma Geological Survey, said Thursday.
Two large earthquakes — one that tied for fourth largest in state history — struck near a town in northwestern Oklahoma less than a minute apart Wednesday night and were followed by 30 smaller quakes through Thursday evening.
"This little burst has been quite remarkable," Boak said. "Having four magnitude 4s in one day is highly unusual. It's up there in that northern center. So it's quite isolated from the ones we had earlier this year and the tail end of last year. But it's definitely of concern."
The United States Geological Survey reported a 4.4-magnitude earthquake about 20 miles northwest of Fairview at 10:27 p.m. Wednesday, followed 30 seconds later by a 4.8 quake less than a mile away. The two temblors were about 3.5 miles deep.
The first quake on Wednesday night was initially estimated to be 4.7 in magnitude but was later revised to a 4.4. Seven smaller earthquakes — still 2.5 magnitude or greater — had occurred earlier in the day Wednesday.
The third largest in the overnight swarm was a 4.0-magnitude quake at 2:37 a.m. Thursday about 17 miles northwest of Fairview. It was recorded about 3 miles deep. Another 4.0-magnitude quake recorded at about 2 p.m. in the same area.
About 9 minutes after the first Fairview seismicity of Wednesday night — the 4.4- and 4.8-magnitude quakes — a 3.4 struck about 20 miles south of Alva, according to the agency. Another 12 minutes later saw a 3.4 occur about 18 miles northwest of Fairview.
The Associated Press reported that Fairview police and Major County Sheriff's Department officials said there were no reports of damage or injuries.
In terms of seismic release, California's is 10 times that of Oklahoma's, Boak said. But this activity is of note, he said.
"We're the capital of the minor league earthquakes," Boak said. "We definitely have more of them. There's no doubt in terms of induced seismicity, we're the epicenter of it, now. It's a really different relationship than most other places that have mainly natural earthquakes.
"But it does mean that as we keep adding more earthquakes, there is steadily more and more risk of having a single earthquake at that higher end."
The seismicity continued rattling the region throughout the day Thursday, ranging in magnitude from 2.5 to 4.0.
And it's not just the first two 4.0-plus quakes that have occurred only seconds from one other.
A 3.0 and 3.5 recorded at 4:48 a.m. were only 24 seconds apart, with each located about 19 miles northwest of Fairview. The stronger of the two was around 3 miles deep, while the other was around 2.5 miles below ground.
Almost all of the quakes since Wednesday night were in the Alva-Fairview area. Alva is in Woods County, and Fairview is in Major County. The two towns are about a 50-mile drive apart.
A 2.8-magnitude quake occurred at 12:42 a.m. Thursday near Edmond, and a 2.6 quake occurred at 11:59 a.m. Thursday near Perry. The Edmond area had seen four more earthquakes earlier Wednesday.
A swarm of earthquakes in the Edmond area in late December and early January prompted state regulators to direct that the operators of five disposal injection wells within 10 miles of the heart of the new seismicity cut their injection volumes.
Matt Skinner, Oklahoma Corporation Commission spokesman, said Thursday that he could not provide an exact number of injection wells in the area of the most recent earthquake swarm, but he said "that is a region that has seen a sharp increase in disposed water over the past couple of years."
The 4.8 earthquake falls shy of Oklahoma's largest recorded quake — a 5.6 centered near Prague in 2011 — but ties for fourth largest ever recorded in the state, if verified, according to data from the Oklahoma Geological Survey.
Wednesday's 4.8-magnitude quake shares fourth place with two other 4.8 temblors recorded near Prague on Nov. 5 and Nov. 8, 2011, according to the data.
Scientists have expressed concerns that Oklahoma might be in line for a larger, more damaging earthquake of 5.0- or even 6.0-magnitude.
Daniel McNamara, a USGS research geophysicist at the National Earthquake Information Center, is one of those experts. In a November interview with the Tulsa World, McNamara cautioned that the hazard is real for another Prague-sized quake that could strike a population center or critical infrastructure.
McNamara described the number of magnitude 4s occurring in 2015 as "unheard of in any other similar-sized region on the planet that we know of." Oklahoma's sequences or numbers are typically associated with large earthquakes such as those in Nepal and Japan, he explained.
“Now we have as many as 13 different fault zones in Oklahoma with magnitude 4s occurring on them this year alone,” McNamara told the World in November. “And so just from the behavior of the Prague sequence, any one of these looks like it could produce a 5- or 6-magnitude earthquake, so we’re very concerned about a number of these fault zones.”
The state has experienced 69 earthquakes of 2.5-magnitude or greater since Oklahomans rang in the new year one week ago, according to USGS data, as of 11:15 p.m. Thursday.
Five of those quakes in 2016 already have been of at least magnitude 4.0. The state notched 29 of those such temblors in 2015 — the highest number yet. There were 14 in 2014 and three in 2013.
2015 easily became the state's most seismic year ever with 907 earthquakes of magnitude-3.0 or greater, according to Oklahoma Geological Survey data. That is a 55 percent jump from 2014's once-banner year, which saw 584 quakes of that size.
The 907 quakes are a 730 percent leap from 2013's final tally of 109, which also was a record high at the time.
World Staff Writers Paighten Harkins and Rhett Morgan contributed to this story.