A leading seismologist has linked the process of shale gas fracking with more than 100 earthquakes that blighted a city in the US Midwest within the space of just 12 months.
Since records began in 1776, the Ohio city of Youngstown had never experienced a single earthquake, until a deep injection well was built to pump waste-water produced by fracking in neighbouring Pennsylvania.
The Northstar 1 site started pumping operation in December 2010 and within the following 12 months seismometers in and around Youngstown recorded 109 earthquakes; the strongest being a magnitude 3.9 quake.
Now leading seismologist Dr Won-Young Kim, the leading research scientist at the Lamont-Doherty Earth Observatory of Columbia University, says the fracking process is directly to blame for the outbreak of earth tremors.
He explained: "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 to 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.
“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."
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 this week in the journal Geophysical Research-Solid Earth.
The first earthquake recorded in the city occurred 13 days after pumping began, and the tremors stopped 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 kilometres beneath the surface,
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.
Two years after it was shut down, the well currently remains abandoned and Youngstown has not been affected by any further earthquakes.