A rare earthquake centered in southern Kansas this week may have been a man-made event caused by oil production activity in that area, according to the Kansas Geological Survey.
"That's the concern," KGS Interim Director Rex Buchanan said. "There have been cases of 'triggered seismicity' in Arkansas and Oklahoma. We're looking to see if that's what happened here."
But Buchanan said it may be hard to determine definitively whether the quake was natural or man-made because it occurred in an area that historically has had some natural seismic activity.
The temblor, which measured 3.8 on the Richter scale, occurred Monday and was centered near the town of Caldwell, about 40 miles south of Wichita, near the Oklahoma border.
Buchanan said there is no evidence yet to suggest the quake was caused by hydraulic fracturing, or "fracking," a process that involves injecting pressurized fluid into a well to fracture the ground and release oil or natural gas.
More commonly, he said, minor quakes related to oil drilling are caused by the disposal of salt water waste from oil drilling operations.
"There's a lot of saltwater produced with oil," he said. "Once you separate that off, you need to dispose of it. In Kansas, that's done in wells deep in the subsurface."
"There is production and disposal wells in the general vicinity around there," he said.
Officials at the Kansas Corporation Commission, which regulates oil and gas production in the state, said it is looking into the issue.
"It is important to point out that Kansas has a long history of oil production with very few reported incidents of any kind," KCC spokesman Jesse Borjon said in an email. "The KCC is looking into the issue of seismic activity as it relates to oil and gas activities. We have been in communication with the Kansas Geological (Survey) and continue to gather information."
Buchanan said there is also a possibility that the earthquake was entirely natural.
Caldwell is in Sumner County, just west of a geological formation called the Nemaha Ridge, a buried granite mountain range that extends roughly from Omaha, Neb., to Oklahoma City.
According to information on the KGS website, that ridge was formed about 300 million years ago and and the faults around it are still "slightly active" today, although most of the seismic activity has been on the eastern side of the ridge, in an area known as the Humboldt fault zone.
"There has been activity down in that part of the state," Buchanan said. "Whether this is a continuation of that or something else, that's what we're in the very early stages of talking about."
The largest recorded earthquake in Kansas, estimated at 5.1 on the Richter scale, hit near Manhattan in 1867. It reportedly toppled chimneys and cracked foundations, and is said to have been felt as far away as Dubuque, Iowa.