YOUNGSTOWN, Ohio - Until last year, this city and the surrounding county had been seismically dead since Scots-Irish settlers arrived in the 18th century.
But on March 17, two minor earthquakes shook the city. And since then there have been nine more - most too weak to cause damage. The latest, on December 31, had a magnitude of 4.0, severe enough to cause minor damage.
Eleven quakes in nine months in a seismically inactive area is unusual. But seismologists found another surprise: most of the quakes' epicenters coincided with the location of a 2,750-meter well.
At the well, a local company has been disposing of liquids from natural gas wells - millions of liters of waste from hydraulic fracturing, a process used to unlock the gas from shale rock.
The location and timing of the quakes led to suspicions that the disposal well was responsible. As wastewater was injected into the well under pressure, the thinking went, some of it might have migrated into deeper rock formations, unclamping ancient faults.
China Daily
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