Earthquakes2011 Oklahoma human-induced earthquake may have triggered larger quake

In a new study involving researchers at the U.S. Geological Survey, scientists observed that a human-induced magnitude 5.0 earthquake near Prague, Oklahoma in November 2011 may have triggered the larger M5.7 earthquake less than a day later. This research suggests that the M5.7 quake was the largest human-caused earthquake associated with wastewater injection.

“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 USGS seismologist and coauthor of the study Elizabeth Cochran.

A USGS release reports that historically, earthquakes in the central United States have been uncommon. Yet in the year 2011 alone, numerous moderate-size earthquakes occurred in Colorado, Texas, Oklahoma, Ohio, and Arkansas. Many of these earthquakes occurred near waste-water injection wells, and some have been shown to be caused by human activities.

The 2011 Oklahoma earthquake sequence included the November 6, 2011, M5.7 earthquake that ruptured a part of the Wilzetta fault system, a complex fault zone about 200 km (124 mi) in length near Prague, Oklahoma. Less than 24 hours prior to the M5.7 earthquake, a M5.0 foreshock occurred on November 5, 2011. That foreshock occurred near active waste-water disposal wells, and was linked in a previously published study to fluid injection in those wells. The earthquakes have not been directly linked to hydrofracturing.

The research published last week suggests that the foreshock, by increasing stresses where M5.7 mainshock ruptured, may have triggered the mainshock, which in turn, triggered thousands of aftershocks along the Wilzetta fault system, including a M5.0 aftershock on 8 November 2011. If this hypothesis is correct, the M5.7 earthquake would be the largest and most powerful earthquake ever associated with wastewater injection. 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.

— Read more in Danielle F. Sumy et al., “Observations of Static Coulomb Stress Triggering of the November 2011 M5.7 Oklahoma Earthquake Sequence,” Journal of Geophysical Research (7 March 2014) (DOI: 10.1002/2013JB010612); also see Katie M. Keranen et al.,”Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7 earthquake sequence,” Geology 41, no. 6 (26 March 2013): 699-702 (doi: 10.1130/G34045.1); and “Wastewater Injection Spurred Biggest Earthquake Yet, Says Study” (The Earth Institute, Columbia University, 26 March 2013)