LITTLE ROCK — Geologists have recorded more than a dozen earthquakes near Quitman this month, but locals haven’t felt many of the smaller ones and they aren’t fearing the ones they do experience.
It’s a change from the concerns residents felt when hundreds of quakes shooknear Greenbrier and Guy along a fault system south of Quitman. Scientists said the recent earthquakes, which are at the northern end of the system, are just a natural continuation of the seismic activity that began last year.
“People are talking about them, but they’re not running around saying, ‘The sky’s falling,’” said Quitman PoliceChief Todd Henry.
Since Oct. 2, at least 18 earthquakes have rumbled under the southwestern Cleburne County town of about 700. A 3.3-magnitude quake Oct. 5 was the largest. Many of the temblors were less than the 2.5-magnitude quakes that people generally notice.
Faulkner and Cleburne counties have seen more than1,200 earthquakes since natural-gas drilling companies began injecting wastewater into 6,000-feet deep wells last summer.
Scott Ausbrooks, geohazards supervisor for the Arkansas Geological Survey, said the injections triggered the quakes. A magnitude-4.7 earthquake Feb. 27 near Greenbrier was the largest Arkansas quake inmore than 30 years.
The Arkansas Oil and Gas Commission banned the use of the injection wells in July and since then, the number of quakes have tapered.
But the ground is still shaking.
“I think this is still the effects of the wells,” Ausbrooks said. “I think we’ll continue tosee more for a while.”
A majority of the earthquakes were centered near Guy and Greenbrier along the southern end of a 10-mile fault system.
The quakes in Quitman are centered at the northern edge of the system.
Ausbrooks said the Quitman quakes are nothing to be alarmed at; it’s energy migrating north from the original epicenters.
“We’re seeing the same pattern that we saw in the southern end,” he said. “We have a build up of a series of quakes popping. Then there’s one significantly sized one that has a triggering effect of several smaller ones.
“The smaller ones are the after-effects of the activity,” he said.
He compared the quakes in Faulkner and Cleburne counties to those that shook along a fault system near Denver in the 1960s and 1970s. Workers injected wastewater into wells during construction of the U.S. Army’s Rocky Mountain Arsenal in 1966. It took seven years before the earthquakes stopped after drilling was completed, he said.
Geologists will install monitors along the northern edge of the fault system to continue studying the Quitman quakes.
One monitor will be placed near Center Ridge in eastern Conway County. A second one will be placed along Arkansas 124 east of Quitman.
“We’ll see some more activity,” he said.
Residents in the area talk more about their theories of what’s causing the earthquakes than expressing any fear about them.
“Most think it’s the fracking,” Chief Henry said, referring to the drilling operations in the area. “I’m not a geologist. I don’t know.
“Most everyone has felt one or more of them, but it’s not affecting anyone’s life,” he said. “Most everyone is living life like they normally do.”
Arkansas, Pages 15 on 10/16/2011