A scientist with the Kansas Geological Survey says an increase in earthquakes in two Kansas counties is linked to saltwater injection from oil and natural gas drilling.

The agency has said in the past that there was a “reasonable probability” that injection wells were linked to an uptick in earthquakes in Harper and Sumner counties in southern Kansas.

The Topeka Capital-Journal reports that KGS scientist Tandis Bidgoli used more definite language Thursday, telling the Kansas Environmental Conference that the two are “certainly linked.”

Bidgoli said the agency wants to more study of the relationship between the increased underground pressure and the quakes. She says scientists want to see if the pressure needs to be dialed back to reduce seismic activity.