LITTLE ROCK — A series of temblors near Greenbrier in central Arkansas, including one Thursday evening, were more likely caused by gas and oil drilling than an active fault, geologists said Friday.
The U.S. Geological Survey reported an earthquake measuring 1.6 in magnitude about 5 miles northwest of Greenbrier at 5:01 p.m. Thursday.
There were no reports of damage.
Several other quakes hit the area over the past several months, said Haydar Al-Shukri, director of the Arkansas Earthquake Center at the University of Arkansas at Little Rock.
Because the earthquakes have occurred infrequently, Al-Shukri believes they are caused by workers drilling for oil and gas in Faulkner County. He expects more, minor ones to rattle the area as drilling continues.
“If it were a fault zone, we’d see constant activity,” Al-Shukri said. “These are occurring sporadically in areas close to drilling and injecting.”
He said drilling and injecting the holes with fluid create pressure underground and cause shifting of tectonic plates.
An area about 8 miles east of Hector in Pope County also has seen an increase in rumblings, he said. The U.S. Geological Survey reported seven quakes measuring 1.8 in magnitude or greater in the past three weeks.
The epicenters of the quakes were at different depths - another indication that they are not fault-based and instead are caused by the drilling, Al-Shukri said.
“When someone extracts oil or injects a lot of fluid into the subsurface, it causes a tip in the balance,” he said. “These quakes are the result of that imbalance.”
Al-Shukri doesn’t expect the earthquakes to be greater than 3.5 in magnitude.
Quakes measuring 4.0 in magnitude can cause minor structural damage.
“We don’t anticipate any problems,” he said. “They are small and most are happening in the middle of nowhere where the drilling is going on.”
Arkansas, Pages 10 on 04/10/2010