After a series of earthquakes has shaken a region just northwest of Morrilton over this past week, geologists and researchers continue to assess the area. Scott Ausbrooks of the Arkansas Geological Survey says his agency and the Memphis-based Center for Earthquakes Research and Information have installed an additional seismic station to follow activity in the area.
Ausbrooks says that although the cause of the temblors is likely natural, his team is looking at a possible connection with nearby injection wells, used in hydraulic fracturing for natural gas.
“You know we've had scattered seismic events in this area in the past but not anything like we've seen as far as frequency and magnitude as of the last week. Two possibilities: one it's natural. Second possibility is there are some injection wells to the northwest of the area, about 8 miles and that is the closest. That is a little bit far but at this time we can't rule anything out.”
He notes the recent pattern of quakes resembles those in Faulkner County 2 years ago which led to the discovery of the “Guy-Greenbrier” fault. The state Oil and Gass Commission shut down four injection wells in the area leading to a significant drop in the number and frequency of earthquakes there.
“I think what you have to have is a specific geological setting. And I think [the area around Morrilton] falls under that criteria. This is a seismically active area. The faults here—or some of them—are oriented favorably to the regional stress. They're most likely pretty near failure anyway. So, it doesn't take much for them to be triggered,” says Ausbrooks.
Two of the earthquakes over the last week measured at 3.4 magnitude and were felt by many residents nearby.