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[Chicago Astronomer - Astro Joe]

How the Earthquake affected Earth

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It is calculated that the Earth is now more round, rotates faster and has moved the pole around a bit. This interesting story from NASA:

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The Dec. 26th Indonesian megathrust earthquake quickened Earth's rotation and changed our planet's shape.

January 10, 2005:

NASA scientists studying the Indonesian earthquake of Dec. 26, 2004, have calculated that it slightly changed our planet's shape, shaved almost 3 microseconds from the length of the day, and shifted the North Pole by centimeters.

Dr. Benjamin Fong Chao of NASA's Goddard Space Flight Center and Dr. Richard Gross of NASA's Jet Propulsion Laboratory said all earthquakes have some effect on Earth's rotation. It's just that the effects are, usually, barely noticeable.

This one was not usual: The devastating megathrust earthquake registered nine on the new "moment" scale (modified Richter scale), making it the fourth largest 'quake in one hundred years.

More here: science.nasa.gov/headlines/y2005/10jan_earthquake.htm?list1069419

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I knew I felt my head spinning, but I do feel more fit.

[Maddad]

I have debated elsewhere whether the Earth rotates faster as a result of this quake. I appear to be a lone voice throwing the BS flag on the idea.

In order for the Earth to rotate faster with the skater model of the quake, a significant mass must move closer to the spin axis of the planet. This happens if the mass moves either toward a pole or toward the Earth's center.

Saying that the quake produced either of these effects is to misunderstand plate tectonics. The motive behind any such movement is upwelling magma at the world's 70,000 kilometers of mid-oceanic ridges. The 1,000 kilometer wedge of plate that subducted in Sumatra did not just decide to leap under Asia on its own; other rock pushed on it, and that rock got pushed by the rock moving away from the ridge.

If you propose that a large mass moved down or poleward in the quake, then an equal mass had to move up or equatorward to produce this effect. The net change would have been zero. It had to be. Otherwise the Earth would have been shrinking with each quake during the last 4,500 million years, and would be a black hole my now!

Interestingly, in the several hundred years before the quake, the toe of the subducting plate bent down, and rock a hundred kilometers away from the boundary bowed upwards. At the moment of the quake these two processes immediately reversed. The toe snapped up and the land behind it lowered. If you average the movement of rock over the several centuries between quakes, you see no net rearrangement of mass on the Earth that would support the skater mode.

[Chicago Astronomer - Astro Joe]

Dave,

You speak interesting debates. I don't know if we are indeed aletered from quakes, but the instruments used to measure things like that seem to tell us so.

What goes in the interior of our planet is pure speculation. Maybe indeed a large magma mass sloshes around like a belly full of cheap beer. And perhaps mega tons of the Earth's substance does cause a miniscule weight shift. Look at Neptune, it rotates on it's side. Maybe something smaked into it, or perhaps it found it's own level and likes reclining on it's side...I know I do.

The subduction was maybe just enough to alter the rotation a couple of microseconds, but add them all up and we might have to add another leap day...or add another beer frame.

Hail the Gregorian calendar.

[Maddad]

Chicago said:

I don't know if we are indeed aletered from quakes, but the instruments used to measure things like that seem to tell us so.

The computer models we run tell us that if we had instrumentation sensitive enough to measure it, then we would measure it. If anyone here is a computer programmer, then they might have run into my good friend GIGO.

[TheCriticalEye]

Yes the earth's rotation has spead up ... Really nothing to actualy have any effect ( thouanths of a sec )
Mankind has also "altered" earths rotation aswell.

Kinda cool how delicate this planet really is.

[Chicago Astronomer - Astro Joe]

Bill,

What do you say man has done to effect the Earth's rotation and in what way?

Arn't we always adding to the 'Weight" of the Earth, by increasing the number of people, (6 billion + now)...a all time high. And debris constantly falling in from space all adds up.

[TheCriticalEye]

The most effect humans have made on earths rotation is by damming water.
you dont have to believe though.

pulseplanet.nationalgeographic.com/ax/archives/01_sciencetemplate.cfm?programnumber=2061

There are other "credible" resources of the matter.

[Chicago Astronomer - Astro Joe]

I need to contimplate on this for a bit.

My knee-jerk reaction is that although we do dam up waterways, it isnt just standing there, we shoot it thru turbines or divert waterways to dryer sections. So the water is still in motion in one way or another.

Hmmm....

[TheCriticalEye]

actually no ...

water is dammed .. deverted and changed from natural route of flow.

since massive amounts of water is changed from its natural course " by mankind" we have made a minuteeffect on earths rotation.



like i said you don't have to believe me i'm just pointing to what the pro's say.