As state regulators continue to study a possible connection between drilling waste disposal wells in Arkansas's Fayetteville Shale and a flurry of minor earthquakes in the area, the tremors continue unabated, including a 4.7-magnitude earthquake Sunday night and at least 19 measurable earthquakes on Monday.
The Sunday night earthquake, which was centered in Faulkner County, was the most powerful to hit Arkansas in 35 years and was reportedly felt as far away as Iowa, though there were no reports of injuries or major damage. The same area, just a few miles northeast of Greenbrier, AR, has experienced a series of earthquakes in recent weeks, most of 2.0-2.5 magnitude, but occasionally stronger. One of the Feb. 28 tremors was a 3.6-magnitude earthquake and a 3.3-magnitude temblor occurred in Faulkner County early Tuesday morning, according to the Arkansas Geological Survey (AGS).
The Arkansas Oil and Gas Commission (AOGC) recently extended a moratorium on the drilling of new disposal wells in the Fayetteville Shale by six months while it collects data to determine whether disposal activities are contributing to hundreds of small earthquakes in the area (see Shale Daily, Feb. 1). The moratorium is due to end July 28, the same day the findings of the study are expected to be taken up by the commission, AOGC Director Larry Bengal told NGI's Shale Daily.
In December a 30-day emergency order banned new disposal wells on fears that tremors in the area were at least partially caused by the injection of well flowback into existing wells. There are currently seven disposal wells operating in the moratorium area, which is 576 square miles in Faulkner County. Applications are pending for two more wells.
Since then much of the earthquake activity, including the Sunday night tremor, has occurred slightly to the southwest, prompting AGS to place two additional seismic monitors in that area, Bengal said.
"It just continues to I guess add data to our dataset. Certainly it has been the largest one that we've had out there," Bengal said of the 4.7-magnitude earthquake. "And it is a different location farther away from where the other earthquakes were occurring. It helps us define what may be the mechanism that's causing the earthquakes...the magnitude of it doesn't change anything."
During the 1980s parts of Arkansas experienced seismic activity that was deemed to be naturally occurring. The latest seismic activity, which started last summer in the Fayetteville, has shown similar characteristics, according to Bengal.