From 1776 to 2011, Youngstown did not record a single earthquake. But from January 2011 to February 2012, 109 tremors were recorded, according to research (pdf) published in the Journal of Geophysical Research: Solid Earth. The strongest quake, on December 31, 2011, had a magnitude of 3.9.
What changed? In December 2010, a well was dug in neighboring Pennsylvania to pump wastewater produced by fracking.
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