A few months ago we spoke with Cliff Frohlich, a seismologist and Associate Director of the University of Texas at Austin’s Institute for Geophysics, about the connection between a recent string of earthquakes and hydraulic fracturing, or “fracking.” In the interview, Dr. Frohlich told us that fracking can directly cause earthquakes, but only in very rare cases. “In the last year, there have been three well-documented earthquakes that occurred during the frack job and were probably related to fracking. They were all small earthquakes – of a magnitude of 2 or 3 – and, considering that there are millions of frack jobs, fracking-related earthquakes are so rare.”
What is causing these earthquakes, then? Deep well injection, the method used to dispose liquid and solid wastes produced during the fracking process. Frohlich explained that earthquakes occur when this industrial byproduct flows into, lubricates, and provokes a fault located in a shale or coal formation.
Scientists at the U.S. Geological Survey announced Thursday that they will corroborate Frohlich’s interpretation in a report they plan to unveil next month. (The study was the subject of an article this week in E&E EnergyWire.) The government-sponsored researchers studied ten years of seismological data and concluded that recent earthquakes can, indeed, be attributed to deep well injection. ”A remarkable increase in the rate of [magnitude-3.0] and greater earthquakes is currently in progress,” the study’s abstract states. “A naturally-occurring rate change of this magnitude is unprecedented outside of volcanic settings or in the absence of a main shock.”
The study also shows that man-made earthquakes aren’t just getting stronger, they’re becoming more frequent, too. Oklahoma, for example, experienced an “abrupt increase” in the number of earthquakes greater than magnitude 3.0, jumping from an average of 1.2 quakes a year for the previous half-century to more than 25 in 2009. The number of earthquakes linked to deep well injection has even surpassed the number of documented cases of drinking-water contamination linked to hydraulic fracturing, another safety concern tied to natural gas extraction.
What this means for the state of Texas is still unclear. Last October, South Texas experienced a magnitude 4.8 earthquake near the Eagle Ford Shale Play, which is home to over 550 injection wells. There have been other earthquakes linked to injection wells in the Barnett Shale in the Dallas-Fort Worth area. The Barnett Shale contains an estimated 40 trillion cubic feet of natural gas, making it the largest onshore natural gas field in Texas and potentially in the United States.