Oklahoma has experienced the most earthquakes thought to be triggered by human activity in the eastern and central United States, according to a new report from the U.S. Geological Survey. Last year, the state registered more quakes of magnitude 3 or higher than California. Los Angeles Times. 24 April 2015.
http://www.latimes.com/local/california/la-me-man-made-quakes-20150424-story.html#page=1