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.
Source: Wikipedia — Guy–Greenbrier earthquake swarm (CC BY-SA 4.0)