Re: pinhole Pinhole: Earth's rotation changed by quake?

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Mon Dec 27 2004 - 12:52:41 PST 

From: "Paul Doherty" <pauld@exploratorium.edu>
Subject: Re: pinhole Pinhole: Earth's rotation changed by quake?
Date: Mon, 27 Dec 2004 12:52:41 -0800
Message-ID: <web-8270018@exploratorium.edu>

Hi Sue

Merry Newton's Birthday.

A huge earthquake willl change the distribution of mass
near the surface of the earth. particularly a huge
subduction quake.

This change in mass distribution will change the moment of
inertia of the earth.

Since anglar momentum is conserved, a sudden change in
moment of inertia will result in a change in the rotation
rate for the earth.

Experiment, sit in a rotatable chair. Hold two bricks one
in each hand with your arms stretched out to the sides.
Have someone start the chair rotating slowly, To mimic the
earthquake pull your arms in quickly and then note the
increase in the rotation rate.

Here is a government siite which mentions the expected
change in rotation from a great quake

http://bowie.gsfc.nasa.gov/ggfc/sbm_cos.html

Paul D

On Mon, 27 Dec 2004 13:23:14 EST
  ASKDRSP@aol.com wrote:
>Hi Paul, Eric and All,
>
>First of all it is devastating for the loss of life
>caused by the tsunamis
>this past weekend and I know this will continue to be a
>topic of much discussion
>in terms of warning systems, etc.
>
>On an earth science point of view, something is being
>mentioned often but
>without explanation on the news ... soooooo:
>
>Can you please explain what the Cal Tech scientists are
>saying when they
>state that the earth's rotation was changed by 8.9 quake
>that hit on Christmas?
>How was the rotation changed, how does this rotation
>change affect the earth
>overall, and what is the best way to explain it to 8th
>graders?
>
>Thanks so much and hope your holidays are joyous ones,
>Sue Pritchard
>
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