OKLAHOMA CITY (AP) - New research suggests that the sharpest earthquake to strike Oklahoma may have been triggered in part by wastewater injection - which if true, would make the 2011 temblor the strongest ever linked to disposal practices within the oil and gas industry.
An industry spokesman says a cause-and-effect cannot be proven because work in the oil patch hasn’t changed much in generations. A study of the same quake last year noted that wastewater had been injected into abandoned oil wells nearby for 17 years without incident.
The magnitude 5.7 quake, centered near Prague, knocked over four spires at a university 17 miles away and shook a college football stadium that moments earlier had held more than 57,000 fans. Fourteen homes suffered significant damage and two people near the epicenter suffered minor injuries. The quake caused at least $4.5 million in damages.
A study published in March in the Journal of Geophysical Research, written by scientists from Brown and Cornell universities, the Lamont Doherty Earth Observatory at Columbia University, the University of Southern California and the U.S. Geological Survey, concentrated on Oklahoma quakes in the fall of 2011. The state has had thousands of smaller temblors since.
The lead researcher, Danielle Sumy, a postdoctoral student at Southern California and a former USGS geologist, said a magnitude-5.0 quake triggered by wastewater injection early on Nov. 6, 2011, set off subtle pressures that rolled along like dominoes before finding relief in the 5.7 temblor later that day.
“We found that this magnitude 5.0 earthquake did increase the stress in the region around the 5.7 magnitude earthquake, thus allowing a cascade of failure along the fault,” Sumy said.
A recent study linking hydraulic fracturing - the process in which water mixed with sand and chemicals is used to extract oil and gas - to quakes in Appalachia led Ohio agencies to issue new regulations. In Oklahoma, the focus is on the industry’s wastewater, which is often injected into old oil wells for disposal, not on fracking.
“These earthquakes had absolutely nothing to do with hydraulic fracturing, we can say that with confidence,” said Austin Holland, a research seismologist with the Oklahoma Geological Survey, which was not involved in the study. “They may be related to wastewater disposal, but we don’t know. It’s a challenge to separate these things when we can’t see inside the earth.”
Until 2009, Oklahoma averaged about 50 small earthquakes a year. The U.S. Geological Survey says the state is now the most second most-active seismically, behind California. It’s had 116 earthquakes recorded in the last week alone, according to the Oklahoma Geological Society.
Since the infamous New Madrid quakes of 1811-12, the Prague temblor was the second-strongest east of the Rocky Mountains, behind the 5.8-magnitude quake in Virginia that damaged the Washington Monument in 2011.
Until the set of Nov. 5, 2011, quakes, Oklahoma’s last magnitude 5.0 temblor occurred in 1952.
Officials from the Geological Survey say they’re open to the idea that human actions may have caused the increase, but that it could also be completely natural - they just don’t have enough conclusive evidence.
Brian Woodward, the vice president of regulatory affairs for the Oklahoma Independent Petroleum Association, said the industry was working with researchers but that the recent increase in earthquake activity cannot necessarily be blamed on the state’s top industry.
“Granted, we’ve not seen this level of seismic activity in Oklahoma in the last 60 to 80 years and before that we don’t have a record. It causes us all concern, but the rush to correlate this activity with our industry is something we don’t believe is necessarily fair,” he said.
“Our industry has not fought back on proposed regulations and doing more data collection with the geological survey, and we support additional seismic (monitoring).”