Hough, Susan E. ; Page, Morgan (October 20, 2015). "A Century of Induced Earthquakes in Oklahoma?". U.S. Geological Survey. Retrieved November 8, 2015. "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."
