Chile Quake May Have Shortened Our Days (No, Really)

NASA is reporting that Saturday's massive earthquake in Chile may have actually shortened our days because it actually managed to push the Earth off its axis by as much as 3 inches.

Scientists using complex computer models have calculated that the quake should have moved Earth's figure axis (the axis on which Earth's mass is balanced) by 2.7 milliarcseconds (3 inches). Earth’s figure axis is not the same as its north-south axis; they are offset by about 33 feet. Scientists say this shift will shorten the day by about 1.26 microseconds (a microsecond is one millionth of a second.) But while it's a teeny, tiny amount of time, it's nonetheless permanent.

The same group of scientists estimated that the 9.1-magnitude earthquake in Sumatra in 2004 likely shortened the day by 6.8 microseconds, shifting the Earth's axis by 2.32 millarcseconds (2.76 inches.) Even though the Chile quake was much smaller than that one, scientists say that it affected the Earth's axis because it was further away from the equator and thus more destabilizing. Also, the fault line responsible for the Chile quake is at a slightly steeper angle, making it more effective at shifting the earth vertically.

Time has a (relatively simple) explanation of how this axis shifting results in shorter days, but it requires a short lesson in physics: Basically, every single point on the planet takes 24 hours to rotate around the Earth's north-south axis, but some parts have to spin faster than others to make the 360 degree spin in that time because of a difference in circumference. (The Equator is 24,901 miles in circumference, while the Arctic Circle is just 9,945 miles.)

An earthquake can alter the Earth's rotational speed in two ways: either by causing it to bulge in places it didn't bulge before, or by shifting it on its figure axis. According to Time, "The law of conservation of angular momentum, however, requires that even under these exigent circumstances, the Earth's angular momentum stays constant, which means the planet must step on the gas (or the brake) to accommodate shifting mass."

Of course, none of this will affect us in any significant way and we for one think it's comforting to know that at least the planet's "angular momentum" will remain constant — not to mention that the Earth is so good at compensating for these shifts, even if it means our 24 hours are diminished.

Photo by NASA via Wikipedia Commons.