Fracking-triggered earthquakes could become stronger over time as more wastewater is injected deep underground, new research suggests. It follows the release of several studies linking hydraulic fracturing directly to increased seismic activity.
Scientists attending the Seismological Society of America (SSA) annual meeting Thursday said that underground disposal of wastewater and fracking likely induce earthquakes by changing the state of stress on existing faults to the point of failure. Most seismic events linked to fracking had been magnitude 3.0 or less.
Researchers had previously believed that such induced earthquakes could not exceed magnitude 5.0. But in 2011, two stronger earthquakes were recorded in heavily drilled areas near Trinidad, Colorado and Prague, Oklahoma.
The larger quakes led researchers brought together by the SSA meeting to believe there may be a cumulative effect and that larger, "outlier" earthquakes could become the norm.
“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,” Gail Atkinson, professor of earth sciences at Western University in Ontario Canada, said at the SSA meeting.
Fracking is the process of injecting large volumes of water, chemicals, and sand at high pressure deep underground to dislodge oil and gas. Afterward, wastewater from the process is shot even deeper underground for storage.
Several studies have linked earthquakes directly to fracking activities, and as fracking increases in the U.S. so too does the number of earthquakes — especially in heavily drilled areas. The United States Geological Survey (USGS) recorded five times more earthquakes over magnitude 3.0 on average annually from 2010-2012 compared with years 1967-2000.
Over time, as more wastewater is sequestered underground, larger faults further away from the well site could be triggered, creating stronger earthquakes tens of miles from fracking sites.
“With these huge wells, the pressure they create can travel tens of kilometers,” said Katie Keranen, assistant professor of geophysics at Cornell University, who led the study on the Jones earthquake swarm in Oklahoma.
Earthquake swarms, where multiple quakes of around magnitude 3.0 occur almost simultaneously, have hit in Oklahoma in recent years, surprising residents not used to regular seismic activity.
Scientists say that fracking-induced earthquakes don’t necessarily occur in the same area that’s being drilled or where wastewater is being disposed.
“Core pressure models show that they have a much larger impact, and that propagates away from the well,” Keranen said.
This leads to uncertainty among officials and regulators who are trying to protect the safety of residents who live in heavily drilled areas as well as sensitive buildings like hospitals or nuclear facilities.
“We don’t have the data to tell us what the expected ground motions could be — that’s critical information in order for us to evaluate whether an existing facility could be at risk of structural damage from induced seismicity,” Atkinson said.
Scientists have determined the most likely cause of induced earthquakes is wastewater disposal, and to a lesser extent, fracking itself. Wastewater disposal is typically much deeper than where the oil and gas is drilled.
“We do know, based on known injection rates, that pressure would rise high enough to trigger an earthquake, Keranen said. “There’s a really strong correlation.”
Injection rate is the pressure at which the water is shot underground.
Art McGarr, a USGS geophysicist, said, “the volume of injected fluid seems to be the factor that limits the magnitude, whereas the injection rate controls the frequency of earthquake occurrence.”
It’s not the only cause of induced earthquakes, the researchers said, but because the phenomenon has become so widespread, scientists believe it is the predominant cause.
Research also suggests that the biggest wells contribute about 85 percent of the pressure changes that can lead to earthquakes. With more information, industry could theoretically adjust fracking technology to avoid inducing seismic activity, the scientists said at the meeting.
But when it comes to regulation, there appears to be a wide gap in policy.
“There’s quite an absence of regulatory framework in terms of how to evaluate the hazard and who’s responsible for assessing and responding,” Atkinson said.
The USGS, EPA, and the U.S. Army Corps of Engineers are all currently researching induced earthquakes and their causes, the panel said. The USGS is carrying out a first of its kind study this year, creating a seismic hazard map based not only on naturally occurring earthquakes, but also ‘induced’ earthquakes, such as those triggered by fracking activities.
The scientists said more information is needed to better understand induced earthquakes. While industry actors must report some information, scientists say this data is insufficient and not made publicly available often enough.
“There are minimums in terms of what needs to be recorded — injection pressure and volume — but these are only made available to the public once a year,” Rubenstein said. “We need more information reported more frequently to do the science correctly.”