A pair of magnitude-3.9 earthquakes rumbled through central Arkansas this week, about a month after two companies halted operations at nearby injection wells over concerns that they may be linked to the seismic activity plaguing the region.
The latest big quake struck near Greenbrier on Friday morning, less than 24 hours after an equally strong quake hit nearby, according to the U.S. Geological Survey. Officials said no one was hurt and damage was minimal.
The quakes are the largest in the area, about 35 miles north of Little Rock, since the companies agreed to temporarily cease operations at the wells at the behest of the Arkansas Gas and Oil Commission. The wells, used to dispose of wastewater from natural-gas production, ceased operations on March 4.
Their owners _ Oklahoma City-based Chesapeake Energy and Clarita Operating _ have said they don't think the injection wells are tied to the earthquakes. And with the latest rash of quakes, some people in Greenbrier, including police dispatcher Steve Priddy, are questioning the potential link as well.
"I'm not sure that it is the injection wells," Priddy said.
But Scott Ausbrooks, a geo-hazards supervisor for the Arkansas Geological Survey, said it would be premature to rule out a possible tie to the injection wells.
"We're only a month out after they stopped injecting," Ausbrooks said.
The Fayetteville Shale, an organically rich rock formation underlying the region, is a major source of natural gas in Arkansas. Drillers free up the gas by using hydraulic fracturing or "fracking," which requires injecting pressurized water to create fractures deep in the ground. The two injection wells at issue dispose of "frack" water when it can no longer be re-used by injecting it into the ground.
Dozens of smaller earthquakes have been shaking the town in recent weeks _ part of a series of about 1,000 quakes to hit the region since September. The largest of those _ with a magnitude of 4.7 on Feb. 27 _ was the biggest quake to hit the state in 35 years. Neither of the larger quakes this week caused much damage _ or even disruptions in traffic, Priddy said.
"We've gotten pretty used to them around here lately," he said.