Ohio earthquakes tied to a deep wastewater disposal well are raising safety questions, amid a nationwide natural gas drilling boom. On New Year’s Eve, a magnitude-4.0 quake outside Youngstown, Ohio, shook the ground as far north as Toronto. Earthquake experts tied the event, the latest and largest in a series stretching back to March, to a 1.7-mile-deep wastewater disposal well, prompting state officials to shut it down. "Earthquakes may continue there for years," says seismologist Won-Yong Kim of the Lamont-Doherty Earth Observatory at Columbia University in New York City.