Earthquakes induced by the injection of wastewater, such as that from oil and gas drilling, can cause larger quakes, suggests new research that examined quake activity in Oklahoma.
"The observation that a human-induced earthquake can trigger a cascade of earthquakes, including a larger one, has important implications for reducing the seismic risk from wastewater injection," said U.S.Geological Survey (USGS) seismologist and coauthor of the study Elizabeth Cochran.
The research showed that a magnitude 5.0-magnitude injection-induced quake near Prague, OK in 2011 (see Shale Daily, Oct. 25, 2013), could have triggered a 5.7-magnitude quake less than a day later. If this is the case, the 5.7-magnitude quake could be the largest injection-caused earthquake.
Quakes in the central United States were relatively uncommon until recent years. In 2011, "numerous moderate-size earthquakes occurred in Colorado, Texas, Oklahoma, Ohio and Arkansas," USGS said. Many of these were near wastewater injection wells, and some of the quakes have been the result of human activities, researchers found.
The 5.7-magnitude quake in Oklahoma on Nov. 6, 2011 ruptured part of the Wilzetta fault system, which is about 124 miles long, near Prague. The foreshock to this quake happened on Nov. 5 near an active wastewater disposal well. This quake had been linked to by a previous study to fluid injection. These quakes have not been directly linked to hydraulic fracturing oil/gas well stimulation, USGS said.
A quake with a magnitude of 5.5 to 6.0 is strong enough to cause slight damage to buildings and other structures, while one with a magnitude of 6.1 to 6.9 can cause a lot of damage in very populated areas. A quake of 5- to 5.9-magnitude is classified as "moderate," while one of 6- to 6.9-magnitude is considered to be "strong."
Research published in the Journal of Geophysical Research suggests that the foreshock triggered the 5.7-magnitude quake and in turn triggered thousands of aftershocks along the Wilzetta fault system, including a magnitude 5.0-magnitude aftershock on Nov. 8, 2011.
"If this hypothesis is correct, the magnitude 5.7 earthquake would be the largest and most powerful earthquake ever associated with wastewater injection," USGS said. "All three earthquakes of magnitude 5.0 and greater along the Wilzetta fault exhibited strike-slip motion at three independent locations along the fault, suggesting that three separate portions of the Wilzetta fault system were activated."
A large majority of Oklahoma’s earthquakes over the past three years have been centered on two counties, according to Oklahoma Geological Survey data. There were 1,781 earthquakes recorded in Oklahoma County and another 1,458 in neighboring Lincoln County between January 2011 and February 2014. No more than 371 quakes were recorded in any other county during that time.
Besides USGS, researchers from the University of Southern California, Cornell University, Brown University, and the Lamont Doherty Earth Observatory at Columbia University participated in the study.