Since You Asked: Quake did slow down rotation of the Earth ... a little bit

Shortly after the earthquake in Chile on 27 February 2010, multiple news sources reported that the quake may have affected the length of the Earth's day by 1.26 microseconds.

As far as I can figure, the only way to shorten the day is for the Earth's rotational period to be shorter, which means the planet is spinning faster. I doubt this, but I wouldn't really know. I do know that over the eons the Earth is gradually slowing, so the day is lengthening marginally. Can you look into the real situation here?

— Chuck S., Ashland

Well Chuck, NASA confirms that the Chilean earthquake of magnitude 8.8 may have shortened the length of Earth's day by 1.26 microseconds.

Just to show that we know people in high places, we contacted Dr. Russ Evans of the British Geological Survey and he confirmed that earthquakes can change the length of days.

In an e-mail, he wrote, "This is because they make small changes to the distribution of mass (just the distribution, not the total mass) of the Earth, changing its moment of inertia. Parts of the Earth's surface and the material beneath can be lifted up, and other parts pushed down."

He said such geometrical changes can lengthen, shorten or make no changes to the length of a day.

Evans went on to say that "on average, the net long-term effect of earthquakes on the length of day is practically zero." He also said that "all these variations are simply small corrections to the rate of slowing caused by the principal long-term process of tidal locking," with tidal locking increasing the length of day by around 2 microseconds per century.

Tidal locking is the process by which two bodies in an orbital relationship will, over time, come to show the same face to one another. The moon is already tidally locked on the earth. As the earth continues to slow, after a few gazillion years it could become tidally locked on the moon (and when that happens, you'll read it here first).

To sum it all up, Evans said, "The effect of large earthquakes . . . is to add a small short-term variation to the steady lengthening of the day due to tidal locking."

OK, we have to go rest our brains in a dark room for awhile to recover from this answer.

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