Heather Savage was struck by the date of the Oklahoma earthquake -- Feb. 27, 2010. At magnitude 4.1, it wasn't all that big or damaging. But it was the same day as one of the largest earthquakes ever recorded, a magnitude-8.8 rupture that killed more than 500 people and wreaked havoc thousands of miles south in Chile. "They were only about 16 hours apart," said Savage, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. Savage and her fellow researchers at Lamont-Doherty now believe a "seismic wave" from that megaquake set off the smaller quake near Prague, Okla.