Despite the enormous increase in earthquakes in Oklahoma that started at the same time as heavy fracking began there—with the number of earthquakes over 3.0 magnitude skyrocketing from an average of less than two a year to 585 last year—the state has been in official denial about the cause.
Ecowatch, April 23, 2015.
http://ecowatch.com/2015/04/23/oklahoma-earthquakes-caused-by-fracking/