NASA scientists claim that the massive earthquake that shook Chile on Saturday may have shifted Earth's axis by about 3 inches (8 centimeters) and shortened its days by about one-millionth of a second. The length of a day is determined by the amount of time it takes the planet to complete a full rotation. Earthquakes can affect the Earth's rotation speed by shifting some of the planet's mass closer to or further from its axis. This is not the first time an earthquake has had such an effect. According to computer models, the 2004 Indian Ocean earthquake should have shifted the Earth's figure axis by 2.76 inches (7 centimeters) and shortened its day by 6.8 millionths of a second.