Guy-Greenbrier earthquake swarm

The Guy-Greenbrier earthquake swarm occurred in central Arkansas beginning in August 2010. The epicenters of earthquakes in the swarm showed a linear distribution, with a clear overall shift in activity towards the southwest with time, and the largest event in the swarm was the 2011 Arkansas earthquake, at 4.7 on the moment magnitude scale.

Cause
It has been suggested that the swarm was triggered by drilling activities associated with the exploration and production of shale gas in the Fayetteville Shale in northern Arkansas. Analysis of the swarm has found no link between this relatively shallow drilling and the earthquakes, but has instead suggested a link with deep waste disposal drilling similar to that identified at the Rocky Mountain Arsenal in the 1960s, and has led to a moratorium on such drilling being proposed covering an area of 1150 mi2.