Officials say Oklahoma had more earthquakes last year than in the past 30 years.

The U.S. Geological Survey says 567 earthquakes with magnitudes of 3.0 or greater were registered in Oklahoma, making it the most seismically active state in the nation, excluding Alaska and Hawaii.

The 2014 total is five times greater than that recorded in Oklahoma in 2013. Seismologists say it’s unclear whether the increase in the number of earthquakes is a trend that will continue into 2015.

The Tulsa World reports that the rise in quakes has raised suspicion as to whether hydraulic fracturing, an oil and gas drilling method also known as “fracking,” is responsible for the uptick.