Geologists are studying two small earthquakes that rattled northern and eastern Arkansas on Monday and Tuesday to determine if they were caused naturally or by natural gas injection wells.
The first temblor occurred at 2:16 p.m. Monday about 10 miles west of Fairfield Bay in Van Buren County. It registered 2.7 in magnitude, said Scott Ausbrooks, geohazards supervisor for the Arkansas Geological Survey.
The quake was strong enough to knock books off of shelves at the library in Clinton, about 5 miles south of its epicenter. Several people in the area also reported hearing rumbling, Ausbrooks said.
“It was close to the surface,” he said of the fault system that spawned the earthquake. “That’s a good amount of shaking for an earthquake that size.”
Earthquakes of 2.5 in magnitude or less generally go unfelt, he said.
The geological survey installed seismic monitors in the area in 2012 after scientists determined that gas drilling companies injected wastewater into wells and caused hundreds of earthquakes in Faulkner and Van Buren counties.
There are two wells near the epicenter of Monday’s quake, he said.
Ausbrooks said he was uncertain if Monday’s temblor was caused by an injection well, changes in the levels of nearby Greers Ferry Lake or a natural fault slippage.
“We’ve not reached any conclusions yet,” he said. “We’re not ruling anything out.”
On Tuesday, geologists also recorded a 2.6-magnitude quake 2 miles northeast of Cherry Valley. It occurred at 5:55 p.m., and people along Arkansas 42 just east of the Cross County town reported feeling it, said Cherry Valley PoliceChief Buck Morris.
“They said they felt some minor shaking along the ridge,” Morris said, referring to Crowley’s Ridge - a formation of windblown soil deposits that runs through eastern Arkansas.
“It’s not that common for earthquakes to happen along the ridge,” Ausbrooks said.
A quake registering 3.9 in magnitude rumbled beneath Parkin about 20 miles to the southwest of Cherry Valley on Oct. 29, 2012, and was felt in five states.
Geologists have studied the area in the past to try to determine if faults that run beneath the earth are part of the New Madrid seismic zone or if they are from another system.It remains unclear. The New Madrid zone runs from southern Indiana southwest to near Marked Tree and triggered a series of huge earthquakes in 1811 and 1812 that rang church bells in Charleston, S.C., and was felt as far as Washington, D.C.
Northwest Arkansas, Pages 14 on 02/02/2014