Thousands of times every day, drilling deep underground causes the earth to tremble. But don't blame the surprise flurry of earthquakes in Oklahoma on man's thirst for oil and gas, experts say.
Oklahoma residents more accustomed to tornadoes than earthquakes have been shaken by weekend temblors that cracked buildings, buckled a highway and rattled nerves. One quake late Saturday was the state's strongest ever and jolted a college football stadium 50 miles away.
The East Coast doesn't get earthquakes often but when they do strike, there's a whole lot more shaking going on. The ground in the East is older, colder and more intact than the West Coast or the famous Pacific Ring of Fire. So East Coast quakes rattle an area up to 10 times larger than a similar-sized West Coast temblor.
The massive earthquake that struck off the coast of Japan Friday ranks as the fifth largest in the world since 1900, scientists said.
