Seismologists believe a pair of earthquakes that rocked Ohio recently may have been the result of the controversial natural gas extraction process known as hydraulic fracturing, or fracking. A 4.0-magnitude earthquake shook the city of Youngstown Saturday, one week after another quake shook a nearly identical location. Both sites are at the bottom of a 9,200-foot-deep disposal well where waste from fracking had been injected under pressure. The quakes were the 10th and 11th to occur near the well since March. Links between fracking sites and earthquakes have also been noted in Texas, Arkansas, Colorado and Oklahoma.