CERI Public Statement on the Guy Earthquake Swarm
A magnitude 4.7 earthquake occurred near the town of Greenbrier in central Arkansas on Sunday night February 27, 2011 at about 11:01 PM CST. Since that time 36 earthquakes greater than magnitude 1.9 have occurred in the Greenbrier area including 13 events greater than magnitude 2.4. The magnitude 4.7 was the largest earthquake to date, in the continuing earthquake swarm in the Guy-Greenbrier area known as the Guy earthquake swarm. This swarm includes thousands of small earthquakes between Guy and Greenbrier, AR, that began in August, 2010. Central Arkansas has a history of earthquake activity with a swarm of thousands of earthquakes smaller than magnitude 4.5 to 4.7 in the early 1980s and another swarm in 2001 (known as the Enola earthquake swarms), so the current earthquake-rate increase may simply be due to a natural cycle.
Researchers at the University of Memphis, Center for Earthquake Research and Information are investigating the source of these earthquakes and their possible relationship to natural gas production. Our research indicates an earthquake source zone that is large enough to produce a magnitude 5.7 earthquake.
Deep waste water injection, one aspect of natural gas production practice in the Greenbrier/Guy, AR, area, has been shown to cause earthquakes in two well-documented cases in Colorado. Although there is only circumstantial evidence that links current earthquakes with waste water injection in central Arkansas, we are concerned that continued operation of injection wells in the seismic area risks triggering more and possibly larger earthquakes.
Arkansas Earthquakes (University of Memphis video, 2/18/2011)
Poster of the 2010 - 2011 Arkansas Earthquake Swarm