"Ausbrooks said geologists are still trying to discover the exact cause of the recent seismic activity but have identified two possibilities.
"It could just be a naturally occurring swarm like the Enola swarm, or it could be related to ongoing natural gas exploration in the area," he said.
A major source of natural gas in Arkansas is the Fayetteville Shale, an organically-rich rock formation in north-central Arkansas. Drillers free up the gas by using hydraulic fracturing or "fracking" – injecting pressurized water to create fractures deep in the ground.
Ausbrooks said geologists don't believe the production wells are the problem, but rather the injection wells that are used to dispose of "frack" water when it can no longer be re-used. The wastewater is pressurized and injected into the ground." More>>>>