LAWRENCE (AP) — The Kansas Geological Society is investigating whether a recent earthquake in southern Kansas might have been caused by oil production in the area.

But KGS interim director Rex Buchanan said it might be hard to ever determine if the 3.8 earthquake Monday near Caldwell was man-made or caused by natural forces.

Buchanan said there is no evidence yet to suggest hydraulic fracturing caused the quake. He says it’s more common for minor quakes near oil production sites to be caused by the disposal of salt water waste. In Kansas, the salt water waste is disposed of in deep wells.

The Lawrence Journal-World reported the Kansas Corporation Commission, which regulates oil and gas production in the state, is also investigating the issue.