A Marcellus Shale gas drilling tower in Pennsylvania. (CC/Ruhrfisch)
Since records began in 1776, Youngstown, Ohio had never been shaken by an earthquake, until the Northstar 1 deep injection well was built to pump wastewater produced by fracking in Pennsylvania.
In December 2010 the Northstar 1 came online, and in the year that followed 109 seismic events were recorded at Youngstown.
"The earthquakes were centered in subsurface faults near the injection well," said Dr. Won-Young Kim. "These shocks were likely due to the increase in pressure from the deep waste water injection which caused the existing fault to slip."
Waste fluid generated during shale gas production, or hydraulic fracturing, is pumped underground by the deep injection well.
Researchers found that the onset, cessation, and dips in seismic activity correlated to activity at the Northstar 1 well. Their findings are published in Geophysical Research-Solid Earth.
The first earthquake recorded in the city occurred 13 days after pumping began, and tremors ceased shortly after the Ohio Department of Natural Resources shut down the well in December 2011.
The strongest earthquake, magnitude 3.9, occurred on December 31, 2011. Twelve total events registered above 1.8 magnitude. Main shocks occurred at depths of 3.5 to 4 kilometers, deep in the layers known as the Precambrian basement.
Dips in seismic activity occurred for Memorial Day, the Fourth of July, Labor Day, and Thanksgiving holidays as well as other scheduled stops at the well.
Researchers concluded that deep well fluid injection "induced seismic activity" at the Northstar 1 site.
"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."
Two years after it was shut down, the well remains shuttered and abandoned. Ben W. Lupo, owner of Northstar Disposal LLC. which operated the Northstar 1 well, was charged with violating the Clean Water Act in an unrelated case.