The earthquakes that have been linked to oil and gas development so far might be minor, but they could be putting states like Oklahoma and Kansas at risk for a major earthquake later on, new research indicates.
The research, which hasn’t yet been published, was presented at the American Association for the Advancement of Science by U.S. Geological Survey scientist William Ellsworth. Ellsworth said that states in which small, hydraulic fracturing-related earthquakes are a fairly regular occurrence shouldn’t “expect a large earthquake tomorrow,” but they should know that these small earthquakes could increase the risk of a larger, more damaging one occurring eventually.
“The more small earthquakes we have, it just simply increases the odds we’re going to have a more damaging event,” Ellsworth said.
The process of extracting oil and gas has been linked by multiple studies to increased incidence of small earthquakes. Many of these studies blame the process of wastewater injection, a process in which oil and gas companies pump the wastewater used in fracking wells deep underground. The injection of the water can increase fluid pressure underground, making it easier for faults to slip and cause an earthquake. According to one study, nearly all of the 2,500 earthquakes that occurred over a five-year span in Oklahoma could be linked to the wastewater injection process.
But fracking itself — which involves injecting water, chemicals, and sand underground to break apart shale and unlock natural gas deposits — has also been found to have triggered earthquakes: an October 2014 study concluded that 400 small earthquakes in Ohio were triggered by fracking.
And earlier this year, scientists proved for the first time that an earthquake strong enough to be felt by humans was triggered by fracking. The magnitude 3.0 earthquake that occurred in Ohio was, study co-author Robert Skoumal said, one of “the largest earthquakes ever induced by hydraulic fracturing in the United States.”
The degree to which fracking and wastewater injection has contributed to earthquake numbers is, in some states, striking. Last year, Oklahoma experienced three times more magnitude 3.0 and higher earthquakes than California did, with wastewater injection likely being the main driver. And a report last year found that, as oil and gas activity has increased in Ohio, so have earthquakes: between 1950 and 2009, Ohio saw an average of two greater than 2.0 magnitude earthquakes each year. When fracking operations began becoming more common in the state, between 2010 and 2014, that number jumped to an average of nine per year. Nationally, the report found, the country experienced an average of 100 magnitude 3.0 or higher earthquakes each year between 2010 and 2012, compared to just 21 each year between 1967 and 2000.
Mark Zoback, a geophysicist at Stanford University, told Science Magazine that, when it comes to wastewater injection, there are things the oil and gas industry can do to minimize the risk of earthquakes: namely, injecting wasteswater into regions that aren’t near fault lines, or skipping the injection altogether and recycling the water.
Scientists have warned before that the earthquake risks posed by fracking and wastewater injection could get worse: last May, scientists at the Seismological Society of America’s annual meeting said that fracking-induced earthquakes could get stronger and more dangerous in the coming years.
“I think ultimately, as fluids propagate and cover a larger space, the likelihood that it could find a larger fault and generate larger seismic events goes up,” Western University earth sciences professor Gail Atkinson said last year at the meeting.