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    Re: Japan earthquake speeds earth's rotation
    From: Frank Reed
    Date: 2011 Mar 15, 04:51 -0700

    Gary, you wrote:

    "I think this is an error.
    "The closer the mass
    > shift during an earthquake is to the equator, the more it will speed up
    > the spinning Earth."
    moving the mass closer to the center of rotation will cause a speed up due to the "pirouette effect" which is actually a manifestation of the conservation of angular momentum."

    Well, it's not an error, but it's rather poorly described. If you move a mass ten feet away from or towards the axis of rotation, the effect on total angular momentum is greatest at the equator because the speed is greatest there. This can be confusing because away from/towards the axis of rotation are two very different things near the poles and near the equator. Moving a rock ten feet away from the axis when you're near the north pole means rolling it south. Moving a rock ten feet away from the axis when you're near the equator means lifting it up into the air. If you roll a boulder north or south along the ground and assume that its altitude above sea level doesn't change, the biggest changes in total angular momentum will occur at 45 degrees latitude.

    Here's an interesting puzzle: if global sea levels are rising at a rate of about one foot per century (which is what the tide gauges show), how much should the rate of the Earth's rotation be changing?


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