On April 18, 1906, a little after 5 a.m. in San Francisco, California, there occurred a noise that one resident described as being "like the roar of ten thousand lions." And the ground began to shake.
The glass-domed Palace Hotel rained glass and singer Enrico Caruso ran out into the street, said, "Give me Vesuvius" and after indicating his preference for Italy's volcano, left San Francisco forever.
By the time the shaking and resulting fire were over, 500 people had been killed and 3,000 acres in the downtown area had been destroyed.
While earthquakes as bad as the one that hit San Francisco are relatively rare in the United States, there are actually earthquakes almost all the time, perhaps as many as a million a year, but most are too mild to feel.
Earthquakes are caused when the giant plates that make up the Earth's crust rub against one another. The energy released by a large earthquake can be tremendous, scientists say, as much as 10,000 times the energy released by the first atomic bomb.
