Why did the recent earthquake in Chile knock the Earth off its axis and shorten the average day?
Geologic events as large as the recent Chilean earthquake can indeed affect the rate of Earth’s rotation. But the effect is miniscule, with a shortening of the day by only one or two millionths of a second. The great quakes—magnitude 8 and above—only occur about once a year on average. So it would take a million years to shorten the day by one or two seconds—not very significant for daily life! This effect has been going on for much of Earth’s 4.6 billion-year history. The reasons why this occurs are linked to how tectonic plate movement of rock changes the dynamics of rotation. An earthquake is the sudden release of energy from somewhere on or in the Earth, and that energy moves through the Earth as seismic waves. Every year, there are about 500,000 earthquakes, but most are too small to be noticed. Earthquakes can be caused by movements between tectonic plates, along faults that separate two large blocks of rock or even by volcanic eruptions as molten rock moves upward in the Earth’s
