[Phys-L] Re: earthquake

[hhaskell at MINDSPRING.COM (Hugh Haskell)]

At 11:02 -0500 12/30/04, Edmiston, Mike wrote:
> The following quotation is from the Chicago Tribune on-line edition.
>
> * * * <quotation from Tom Skilling> * * *
> Incredibly, the magnitude 9.0 earthquake that struck off Sumatra on
> Sunday morning caused a vertical displacement of so much material that
> the rotation period of the Earth has been permanently altered. By a tiny
> but measurable amount, the Earth is now rotating more quickly on its
> axis, and the 24-hour day is now one ten-thousandth second
> shorter.That's the result of calculations based on preliminary data made
> by Oak Park astronomer Dr. Leslie M. Golden. It's analogous to the
> increase in rotational speed that a twirling ice skater experiences when
> he or she draws in their arms. It is estimated that during the Sumatran
> quake, a block of material roughly 600 miles in length and 100 miles in
> width fell 30 feet closer to the Earth's axis of rotation. The planet
> has responded by rotating more rapidly, albeit ever so slightly, and our
> 24-hour days are now one ten-thousandth second shorter.
Interesting. That number--100 microseconds--is one to two orders of
magnitude larger than others i have seen, which range from one to
three microseconds. I wonder how a large chunk of matter can move
closer to the earth's center without pushing a nearly equal amount
farther away from the earth's center, and thus cancelling out the
first effect, or very nearly so. I would guess that on a scale of 10
meters, the material of the earth is pretty nearly incompressible,
and i doubt that the chunk that was moved fell into a void in the
earth's interior.

While moving a chunk of matter this size could have an effect on the
earth's rotation, I seriously doubt that it is anywhere near as large
as 100 microseconds.

Hugh
--

Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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