The average number of earthquakes of magnitude 3 or greater in the U.S. midcontinent – an area that includes Arkansas, Colorado, Oklahoma, New Mexico and Texas – increased to six times the 20th century average last year, scientists at the U.S. Geological Survey said in an abstract of their research.

The abstract does not explicitly link rising earthquake activity to fracking – known formally as hydraulic fracturing – that involves pumping water and chemicals into underground rock formations to extract natural gas and oil.

But the wastewater generated by fracking and other extraction processes may play a role in causing geologic faults to slip, causing earthquakes, the report suggests.

“A remarkable increase in the rate of (magnitude 3) and greater earthquakes is currently in progress,” the authors wrote in a brief work summary to be discussed Wednesday at a San Diego meeting of the Seismological Society of America.