Over the past 4 years, Oklahoma has been experiencing an unusual upswing of earthquakes. According to the USGS studies show one to three magnitude 3.0 earthquakes or larger occurred yearly from 1975 to 2008, while the average grew to around 40 earthquakes per year from 2009 to mid-2013.
For more information, visit the USGS page on this event.
Oklahoma earthquake activity from Oct 31-Nov 7th. 2013
Credit: USGS
