The rate of earthquakes has increased sharply since 2009 in the central and eastern United States, with growing evidence confirming that these earthquakes are primarily caused by human activity, namely the injection of wastewater in deep disposal wells. A new study by the U.S Geological Survey released today presents evidence that, in addition to these recent earthquakes, most of the larger earthquakes in Oklahoma in the past century may likely have been induced by industrial activities.
This study explores the especially high rates of activity in Oklahoma, the background rate of natural earthquakes in the state and how much the earthquake rate has varied through the 20th century.
"In Oklahoma, seismicity rates since 2009 far surpass previously observed rates at any time during the 20th century," said Susan Hough, USGS seismologist and lead author of the study. "Several lines of evidence further suggest that most of the significant earthquakes in Oklahoma during the 20th century may also have been induced by oil production activities. Deep injection of waste water, now recognized to potentially induce earthquakes, in fact began in the state in the 1930s."
The study uses archival reports at the Library of Congress and drill permit records showing the location of wells from the Oklahoma Corporation Commission to track how wastewater injection evolved over time, with an increase around 1950 due to a rise in secondary oil recovery in response to increasing depletion of fields.
"Waste water injection has a strong correlation to the increase in earthquakes," said Morgan Page, USGS seismologist and co-author of the study. "The results further demonstrate that, while the rates seen in recent years are unprecedented, induced earthquakes are likely nothing new in Oklahoma."
Oil production in Oklahoma has been going on for over 100 years. Some activities related to oil production, particularly disposal of wastewater in deep injection wells, are known to potentially cause earthquakes. Prior to the 2011 magnitude 5.7 Prague, Oklahoma earthquake, the largest historical earthquake in the area was the 1952 magnitude 5.7 El Reno earthquake, which the study concludes was likely induced by activities related to oil production near Edmond, Oklahoma.
The complete research paper, "A Century of Induced Earthquakes in Oklahoma?" by Susan E. Hough and Morgan Page was released online in the journal Bulletin of the Seismological Society of America.