The more oil and gas companies pump their saltwater waste into the ground, and the faster they do it, the more they have triggered earthquakes in the central United States, a massive new study has found.
An unprecedented jump in quakes in America's heartland can be traced to the stepped-up rate at which drilling wastewater is injected deep below the surface, according to a study that looked at 187,570 injection wells over four decades.
It's not so much the average-sized injection wells but the supercharged ones that are causing the ground to shake. Wells that pumped more than 12 million gallons of saltwater into the ground per month were far more likely to trigger quakes than those that put lesser amounts per month, the University of Colorado study found. The study was published Thursday by the journal Science.
The connection makes sense because "high-rate injection creates much higher pressure over the relative time scale," said study co-author Shemin Ge. Other potential factors, such as cumulative amounts of saltwater injected or depth, didn't show up as significant in the researchers' reading of the database.
Although Texas, Arkansas, Kansas and other states have seen increases in earthquakes, the biggest jump has been in Oklahoma. From 1974 to 2008, Oklahoma averaged about one magnitude 3 or greater earthquake a year, but in 2013 and 2014, the state averaged more than 100 quakes that size per year, according to another earthquake study published Thursday in Science Advances. Since Jan. 1, the U.S. Geological Survey has logged more than 350 magnitude 3 or higher quakes in Oklahoma.
Studies have linked the increase in quakes to the practice of injecting leftover wastewater into the ground after drilling for oil and gas using newer technologies — such as hydraulic fracturing, also known as fracking.