Oklahoma Earthquake? Blame Oil and Gas

A new study proves what we’ve suspected all along—oil and gas drilling triggers earthquakes.

June 18, 2015

Photo: Brian Sherrod/USGSDamage to a home in central Oklahoma after a magnitude 5.6 earthquake in November 2011

Oklahoma had 585 earthquakes with a magnitude of 3.0 or higher last year. Before 2008, the state would average one or two.

A study published today by Stanford University geophysicists says oil and gas drilling is responsible for the earthquake surge. The culprit? “Produced water,” the brackish fluid that comes to the surface along with oil and gas and is subsequently reinjected deep within the earth for disposal. If the researchers are correct, it settles a long-running debate about the contribution of oil and gas exploration to seismic activity.

There seems to be an unshakeable link between drilling for oil and earthquakes, both in reality and in the human mind. In a 1944 article, Popular Mechanics explained that energy companies use dynamite to create “miniature earthquakes” to determine whether there is oil in a particular location. (By the way, the article is worth reading for its hilarious concern that World War II would use up all our oil.)

By the mid-1960s, seismologists began to worry that humans were capable of triggering earthquakes unintentionally as well—although the concern wasn’t always oil and gas. For about 50 years, between World War I and the Vietnam War, the United States manufactured chemical weapons. This industry, unsurprisingly, produced some pretty nasty waste. The U.S. Army initially sprayed the stuff onto a confined patch of soil and waited for it to evaporate. Eventually, the military realized that soaking the ground with dangerous chemicals contaminated drinking water. So, in 1961, the army drilled a 12,000-foot well northeast of Denver and began injecting millions of gallons of chemical weapon by-products. In the next five years, seismologists measured more than 700 earthquakes, most of which had epicenters near the well. A geologist speculated that the two were related.

Steven Than/Stanford UniversityIllustrated by: Steven Than/Stanford University

Oil and gas production also involves injecting large amounts of wastewater deep underground, but for years, many scientists disputed that this practice might cause earthquakes. “There is little historic evidence to indicate that injection or withdrawal of fluids during drilling and producing operations causes earthquakes,” the U.S. Bureau of Land Management wrote in a 1978 environmental assessment. The bureau included the same sentence in several publications, suggesting that it was boilerplate language expressing the official agency line.

In 1990, the U.S. Geological Survey published a report to the U.S. Environmental Protection Agency conceding that injecting fluids deep within the earth could cause earthquakes but continued to insist that injection of waste fluids was only rarely to blame. By that time, the consensus had already started to crumble. The Sierra Club claimed in 1989 that it could document cases in which underground injection of wastewater had triggered earthquakes.

The rise of hydraulic fracturing, or fracking, which vastly expanded oil and gas production in the United States, represented a massive, real-world experiment to settle this disagreement. U.S. oil and gas production soared beginning in 2005, and residents of shaky towns in Texas, Oklahoma, and other oil-rich states began to point the finger at fracking. By 2009, seismologists were reporting that there had been more earthquakes around Dallas in nine months than in the previous thirty years combined. A resident in Cleburne, Texas, said, “If it’s not [fracking], it just seems like the biggest coincidence in history.”

Since fracking kicked off the U.S. oil and gas boom, it was reasonable to conclude that it was also causing the earthquakes. If the newly released Stanford study is correct, though, the reality is slightly more nuanced.

There are several fluids involved in the drilling process. Fracking fluid is a water-based chemical solution injected into the ground to create cracks in the shale, allowing the oil and gas to flow out. Flowback water is a mixture of fracking fluid and water present in the rocks, which comes back to the surface during the cracking process. The Stanford researchers say these two fluids, which are what differentiate fracking from traditional oil and gas exploration, are not responsible for the earthquakes—at least not the ones in Oklahoma, the area they studied.

Instead, the problem is produced water, which exists naturally next to oil and gas within the pores of the earth. This water has been associated with all forms of oil and gas drilling for decades, not just fracking. It’s no wonder, therefore, that scientists have for so long been arguing over whether injecting water underground can cause earthquakes—this phenomenon isn’t new, it has just become more noticeable with increased fossil-fuel production.

There had been more earthquakes around Dallas in nine months than in the previous thirty years combined

When drillers force the fossil fuels out, produced water comes along with it. The problem is that this water has no commercial value, so it has to go back into the ground. The location of the reinjection matters. For years, drillers in Oklahoma have been pumping millions of gallons of produced water into the Arbuckle formation, a 7,000-foot-deep layer of sediment that sits on top of a rock layer containing faults. The massive weight of the water increases pressure that affects the underlying rocks, triggering earthquakes.

The good news for Oklahomans is that this understanding should lead to solutions. Oil and gas companies should think more carefully about where to dump produced water. Putting it back into the same area it came from would be a good start, but, at the very least, they should avoid fault-rich regions.

Of course, we could just transition to green energy. Solar cells have never caused an earthquake. 


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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