No. 7: Which Natural Disaster Shortened Earth’s Days?

Feel like the days are getting shorter? Well, they did. On February 27, 2010, the massive 8.8 earthquake centered in Maule, Chile, torqued the earth so hard that our planet’s axis shifted — though not so much that you’d notice. According to scientists at NASA’s Jet Propulsion Laboratory, computer models show that the 2.76-inch shift shaved 1.26 millionths of a second off each day.

And it’s not the first time an earthquake has shortened the day. Geophysicist Richard Gross, the Earth rotation-variation expert (say that three times fast) who calculated the change, also predicted that the 2004 Sumatra-Andaman earthquake, which measured a whopping 9.0 and caused a tsunami that took thousands of lives, shaved 6.8 millionths of a second off Earth’s day.

So, could the day get trimmed again? Sure, but it takes a particular type of quake: Megathrust earthquakes, the most powerful kind known to science. Megathrust quakes occur at subduction zones, where one tectonic plate can be forced under another, creating huge earthquakes, often deforming the ocean floor and tweaking the rotation of our planet.

Megathrust quakes have been reported as far back as the year 365, when the African and Eurasian plates clashed, causing widespread destruction around Crete. The resulting tsunami in Alexandria was documented by Roman historian Ammianus Marcellinus, in the first account of an earthquake followed by a drastic recession of the sea and then a huge wave.

–Jessica Hilberman

Jessica Hilberman is a Yahoo! editor and a die-hard generalist. In her former freelance life, she edited and wrote for an eclectic assortment of publications, including Wired, Sunset, Self, Teen People, DailyCandy,, and even Poultry magazine.