The U.S. Geological Survey (USGS) confirmed a 3.2 magnitude earthquake on Wednesday, two miles southeast of Charlotte, TX in Atascosa County, which is almost entirely in the liquids-rich or oil window of the Eagle Ford Shale. Last week, 13 active rigs were running in the area. According to the USGS, there is evidence that some central and eastern North American earthquakes have been triggered or caused by human activities that have altered the stress conditions in earth's crust. The cause of this most recent quake is unknown; however, in the Eagle Ford Shale and other areas for oil & gas development in Texas, a link has been made between waste water disposal/injection wells and seismic activity.
Injection wells are necessary to the fracking process, a method by which a well is completed using treated water under extreme pressure. When a well is fracked, it produces flowback or produced water that must be disposed of properly in waste water disposal/injection wells deep underground. Recently, EagleFordShale.com posted a story about new waste water disposal rules that could be put into practice soon in Texas, following a rash of low magnitude earthquakes across the state.