The people of Youngstown, Ohio say they never felt an earthquake before two-and-a-half years ago. But between January of 2011 and February of 2012, 109 tremors were recorded and the author of a new article points the finger at hydraulic fracturing - fracking. 

In December 2010, Northstar 1, a deep injection well built to pump wastewater produced by fracking in the neighboring state of Pennsylvania, came online. In the 14 months that followed seismometers in and around Youngstown recorded 109 earthquakes; the strongest was a magnitude 3.9 earthquake on December 31, 2011. Six of them could be 'felt'.

Dr. Won-Young Kim of Lamont-Doherty Earth Observatory, Columbia University, analyzed the Youngstown earthquakes, finding that their onset, cessation, and even temporary dips in activity were all tied to the activity at the Northstar 1 well. The first earthquake recorded in the city 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.

Dips in earthquake activity correlated with Memorial Day, the Fourth of July, Labor Day, and Thanksgiving, as well as other periods when the injection at the well was temporarily stopped.

Those minor tremors happen 900,000 times per year and even the largest recorded in Youngstown happens 30,000 times each year but Kim believes the well is a cause for concern, since they had not been felt before.

"In recent years, waste fluid generated during the shale gas production - hydraulic fracturing, had been increasing steadily in United States. Earthquakes were triggered by these waste fluid injection at a deep well in Youngstown, Ohio during Jan. 2011 - Feb. 2012. We found that the onset of earthquakes and cessation were tied to the activity at the Northstar 1 deep injection well. The earthquakes were centered in subsurface faults near the injection well. These shocks were likely due to the increase in pressure from the deep waste water injection which caused the existing fault to slip," said Kim. "Throughout 2011, the earthquakes migrated from east to west down the length of the fault away from the well—indicative of the earthquakes being caused by expanding pressure front." 

Citation: Won-Young Kim, 'Induced seismicity associated with fluid injection into a deep well in Youngstown, Ohio', Journal of Geophysical Research: Solid Earth Volume 118, Issue 7, pages 3506–3518, July 2013 DOI: 10.1002/jgrb.50247