From NBC News:
Before January 2011, Youngstown, Ohio, which is located on the Marcellus Shale, had never experienced an earthquake, at least not since researchers began observations in 1776. However, in December 2010, the Northstar 1 injection well came online to pump wastewater from fracking projects in Pennsylvania into storage deep underground. In the year that followed, seismometers in and around Youngstown recorded 109 earthquakes, the strongest registering a magnitude-3.9 earthquake on Dec. 31, 2011. The well was shut down after the quake.http://t.nbcnews.com/......
The new investigation of the Youngstown earthquakes, detailed in the July issue of the journal Geophysical Research Letters, reveals that their onset, end and even temporary dips in activity were apparently all tied to activity at the Northstar 1 well.
For instance, the first earthquake recorded in Youngstown occurred 13 days after pumping began, and the tremors ceased shortly after the Ohio Department of Natural Resources shut down the well in December 2011. In addition, dips in earthquake activity lined up with Memorial Day, the Fourth of July, Labor Day, Thanksgiving and other times when injection at the well was temporarily stopped.
"Earthquakes were triggered by fluid injection shortly after the injection initiated — less than two weeks," researcher Won-Young Kim, a seismologist at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., told LiveScience...
