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Analysis of Enola and Greenbrier, Arkansas, Earthquake Swarms: Cause and Effect?


Almost 20 years after a remarkable Enola earthquake swarm of 1982, near the town of Enola, Arkansas, with more than 40,000 micro-earthquakes, a new swarm revisited the same central Arkansas region in 2001. More earthquakes were recorded in 2010 and 2011 at and between the towns of Guy and Greenbrier, referred here as the Greenbrier earthquake swarm. Both swarms are within the Faulkner County about 54 km (34 miles) north of Little Rock. The Enola sequence still have unanswered questions and the Greenbrier swarm raises the possibility to find answers to these questions.

Within the same vicinity of the Enola and Greenbrier earthquake swarms in the eastern Arkoma basin, the first waste disposal well became operational in April 2009, with depths greater than 12,000ft into the "basement" rock. It imaged the then unrecognized NE striking fault between the towns of Guy and Greenbrier. Since then, the area has experienced an increase in magnitude M ≥2.5 earthquakes.

It is known that the Enola swarm was in an intraplate setting and the feasibility of earthquakes in such a setting is not scientifically understood. There were changes in elevation within the graben of the Enola swarm, giving reason to the swarm occurrence. So the question rises, could fluid (waste-water) injection be the triggering mechanism for the Greenbrier swarm? Does the graben uplift answer the Enola swarm concerns? Do the Enola and Greenbrier swarms have similar triggering mechanisms?