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    Re: Japan earthquake speeds earth's rotation
    From: Frank Reed
    Date: 2011 Mar 15, 03:24 -0700

    I agree that the descriptions are confusing. It's really the net motion of the mass that matters. The east-west motion doesn't change the angular momentum. By the way, if you're trying to put this in perspective, or trying to explain it to your friends, consider that typical tectonic plate movements are about four inches per year. So an eight foot jump is equivalent to roughly 24 years of normal motion. Given the size of the quake, honestly I'm surprised it didn't move a lot more than eight feet.

    By the way, all of these changes in rotation rate and axis are well below the normal "noise" for the rotation of the Earth and its axis. If you look at the daily plots from the IERS, there are no jumps at big earthquakes. Apparently, the atmospheric jet streams are among the largest variables in the Earth's angular momentum balance.

    These articles are becoming commonplace. Every time there's a major earthquake someone calls up Richard Gross at JPL and asks him for some numbers. But these numbers are based on calculations and computational analysis. It's good physics, of course, but they're not actually observing this. We had some discussions on NavList after the Chilean earthquake.

    Another matter that's been making some news in the weirder side of things is the question of lunar perigee. This coming Friday is a perigee Full Moon slightly closer than any in a couple of decades. An astrologer claimed a couple of weeks ago that this "supermoon" would cause earthquakes. Of course when the devastating quake occurred off Japan a couple of days ago, the Moon was nowhere near perigee and farther away than normal while the phase was near half full. We all know how this works. If I say "there will be a big earthquake in the next month", I have a fairly good chance of being right even if my prediction is based on flipping coins. Devastating earthquakes are tragically frequent.


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