Posted on 07 Nov 2011
Central Oklahoma was recovering Sunday after a swarm of weekend earthquakes, including the largest in state history, buckled a highway, damaged several homes and left residents worried they may be living on an increasingly active fault.
Mary Reneau, 68, saw her home of 25 years, a two-story brick ranch house six miles northwest of Prague, Okla., battered by the quakes.
"There isn't a room in the house that hasn't sustained damage," Reneau said. "It looks like a bomb fell."
She said she had never felt an earthquake as intense during all her years in central Oklahoma, where she and her husband run a custom hay-baling business on their 440-acre ranch.
The largest in the latest round, a magnitude 5.6, occurred at 10:53 p.m. CDT Saturday, according to the U.S. Geological Survey. The quake caused major damage to at least five homes, according to Aaron Bennett, a Lincoln County emergency management dispatcher. One man reportedly was injured when he tripped and hit his head while attempting to flee his home.
U.S. Highway 62 buckled in at least two places during the quake, but road crews repaired the damage overnight Saturday, Bennett said.
The quake damaged a 40-foot spire at St. Gregory University in Shawnee and ruptured a water pipe in Chandler, dispatchers said.
The temblor was felt as far away as Chicago, Omaha and Austin, Texas.
Paul Caruso, a seismologist with the U.S. Geological Survey in Golden, Colo., said there was no link between Saturday's earthquakes and one that struck Virginia in August with a magnitude of 5.8. He also said there was no indication that the Earth was shaking more than it had in the past.
"There's no statistical inference that seismic activity is increasing. We've just had a lot more quakes in the news because they have occurred where people live," Caruso said.
Reneau said she had noticed an increase in earthquakes during the last two years, and wondered whether it might be connected to oil and gas exploration in the area.
"There's been a lot of drilling," she said.
In August, a research seismologist published a study noting a swarm of earthquakes in January in an area of south-central Oklahoma with active hydraulic fracturing, or fracking, a form of natural gas and oil drilling using pressurized water and other materials.
The researcher at the Oklahoma Geological Survey at the University of Oklahoma in Norman noted 50 small earthquakes, ranging in magnitude from 1.0 to 2.8, had occurred within about two miles of Eola Field, a fracking operation in southern Garvin County.
"There have been previous cases where seismologists have suggested a link between hydraulic fracturing and earthquakes," the study noted. "But data was limited, so drawing a definitive conclusion was not possible for these cases."
Caruso said the study also examined earthquakes in a different part of the state, and that despite concern in Oklahoma, Arkansas, Texas and Pennsylvania, there have been no recent studies he knows of showing that fracking causes earthquakes, a phenomenon that would be considered "induced seismicity."
Caruso said other cases of "induced seismicity," or earthquakes caused by humans, were related to injection wells such as those used by the U.S. military near Denver that were linked to a series of quakes in the 1960s.
But Caruso said he knew of no recent studies showing that fracking caused earthquakes.
"Right now, we don't necessarily see any correlation," he said.
Saturday night's earthquake followed a 4.7 quake originating in the same area earlier in the day. Both occurred on the Wilzetta fault, or Seminole uplift, where rocks move sideways similar to the San Andreas fault, according to Austin Holland, the research seismologist who wrote the fracking report in August.
The state's last big quake, a 4.3 temblor in October 2010, was along the same fault, he said.Faults go through cycles. In California, they see that a lot. Stress takes time to build up. It's just our sequence takes more time to build up," Holland said.
Holland said it was not clear what caused Saturday's two large quakes.
"We don't know enough about this fault system to say," he said.
Holland said his office has three seismic stations with seismometers positioned along the fault, and students were out Sunday morning setting up seven more, including a station in the Reneaus' pasture, "to see what we can find out from any further seismic activity."
Holland said he hoped residents would respond by preparing earthquake kits and undergoing earthquake preparedness training to avoid injuries like those sustained by the man who fled his home instead of ducking for cover.
"I think the awareness is growing," he said. "People need to know what to do."
Reneau said she wasn't sure whether the latest swarm of quakes would prompt more widespread preparedness or simply lead people to move someplace safer.
"You think you can repair and rebuild," she said, but "how long is it going to be before the next one comes?"