At 9:35 p.m. on Saturday, May 30, Greeley, Colorado was struck by a 3.4 magnitude earthquake. Earthquakes are highly unusual in eastern Colorado, raising speculation that it was a “frackquake” — a man-made earthquake stimulated by the disposal of contaminated drilling water in deep injection wells. This disposal technique forces wastewater generated from hydraulic fracturing (fracking) deep into underground rock formations, lubricating layers of rock that would not ordinarily be subject to movement.
Earthquakes are so rare in eastern Colorado that the U.S. Geological Survey (USGS) has labeled the area “aseismic.” The Greeley Tribune reported that the May 30 quake's epicenter was roughly two miles away from two deep oil and gas wastewater injection sites that have not been inspected for two years.
Scientists placed seismometers around the area to try to gather more detailed information on what may have generated the quake and its aftershocks. Colorado currently has very few seismometers in place because earthquakes are so rare in the state.