A magnitude-3.0 earthquake is small, but most people can feel it. Historically, Oklahoma got less than two of those a year, but in 2013 it became two a week. Morning Edition, NPR. 24 April 2015. http://www.npr.org/2015/04/23/401624166/oklahomans-feel-way-more-earthquakes-than-californians-now-they-know-why