Sumatra Quake's effect on Earth's Rotation?

[bobvanx]

Oh, for heaven's sake. Maddad, please stop being so obtuse. Look, I've even drawn a picture to help you visualize that the center of mass for a plate, when it moves away from the equator, will result in the Earth's angular momentum being conserved by speeding up the rotation.<br /><br />The Himalyas are being pushed up and north. If the net mass moved away from the center of the Earth is zero, due to the subduction of the Indian plate, then there will be an increase in the rate of rotation because the mass of the Himalyas is closer to the axis of rotation.<br /><br />And you certainly know as well as I that plates subduct, rotate, and translate, so to hang your entire objection of the subduction and redistribution of mass is flimsy.

 

[remcook]

okay..to recap the discussion as i see it...<br />maddad is basically saying that everything should be in hydrostatic equilibrium. which is correct.<br />BUT, he's also saying that there will be no change in moment of inertia when there is a movement of a plate.<br /><br />am i correct; is that what you're saying maddad?<br /><br />I propose a simple test:<br /><br />suppose a liquid sphere (water, magma), with at the equator something light (a sponge, mountain). The sponge is like an ieberg, partly bove the water. At the column of the sponge, there is less water.<br />Now move the sponge to a pole. there will be an upwelling of water at the place where the sponge used to be.<br /><br />Now, can someone calculate the moment of inerti relative to the rotation axis for both cases?

 

[Maddad]

remcook<br />Yeah, you have it pretty much right. The no change part though is over several decades, not just the instant of the earthquake.<br /><br />bobvanx<br />Hmmm. Interesting that you would bring up obtuse. Lacking quickness of perception or intellect. Your argument fails to preceive that landmass moving poleward on the surface is offset by an equal landmass moving equatorward in the interior. Do you have the intellect to say "no net change"?<br /><br />I'm done with this discussion. It's like politics. Minds are now made up and will not change, regardless of facts. And bob, like politics, I'm right and you're not. Yanno what I mean, jellybean?

 

[bobvanx]

<blockquote><font class="small">In reply to:</font><hr /><p>I'm right and you're not. Yanno what I mean, jellybean?<p><hr /></p></p></blockquote>Yep, I certainly do.<br /><br />I also know that when you point one finger at me, there are three pointing back at you.

 

[Maddad]

Tigerbiten<br />Hmmm. Don't remeber you in this thread before, so I'll drop one more thought before passing on to bigger and better discussions.<br /><br />Remember that material subducts because something pushed on it. It does not subduct, or slide one plate against another, to fill a vacuum. Even two plastic objects may not occupy the same space at the same time. The result still has to be a balance between plates moving in one direction and material moving into its space from another direction.

 

[bobvanx]

<blockquote><font class="small">In reply to:</font><hr /><p>passing on to bigger and better discussions.<p><hr /></p></p></blockquote>Don't let the door hitcha on the way out!<br /><br />Ba-bye!<br /><br />Whew, okay, now that Mr. Right has left the room, we can all breath a sigh of relief that the earth's minor wobblings and perturbations aren't influenced one bit by him. Earth's got no ears, she just keeps on twitching and grumbling, until heat death finally reduces her song to silence.

 

[claywoman]

If I remember from my one lone class on geology, doesn't the earth's rotation often speed up and slow down? I don't believe this has any long term affects on the rotation, but could it alter the journey around the sun slightly? Just wondering....

 

[remcook]

it would not affect its journey around the Sun, since there is nothing that is moving the Earth somewhere else (a force). There's just a shift in mass, thus inertia.<br />

 

[claywoman]

Thank you...i was thinking on the principle of for every action (the slight wobble) there is an equal reaction...just wondered if somehow it would affect it...

 

[bobvanx]

<blockquote><font class="small">In reply to:</font><hr /><p>doesn't the earth's rotation often speed up and slow down?<p><hr /></p></p></blockquote>You recall your geology instructor's instruction pretty well. I don't know about often, but there are lots of forces that change the Earth's rate of rotation. Some occur over geologic timescales, some over the scale of lifetimes or months.<br /><br />For example, sometimes the atmosphere expands due to the sun's activity, and the Earth slows down a little. Sometimes the oceans cool a little bit and so the water is denser, and so the Earth speeds up a little.<br /><br />What we've been discussing here is that an earthquake, since it results in the large-scale motion of mass, also has a measurable effect on the Earth's rotation. It turns out that equatorial zone quakes have so little effect that it's below our threshold to measure. But high-latitude quakes do change the length of our day, by a measurable amount.<br /><br />Far greater than earthquakes are forces such as the Moon, slowing us down through gravitational exchange. Just as the Earth stopped the Moon's apparent rotation, such that it keeps one face towards us, Luna is working on doing the same to us. She steals rotational energy from Earth, and increases the height of her orbit as she does so.<br /><br />I recall reading somewhere that the Earth once had an 18 hour day, when the Moon was about twice as close, and that eventually we'll have a 30 hour day. By then the Moon will be far enough out that the momentum transfer stops being much of a factor.

 

[bobw]

What did you use to make that nifty drawing?<br /><br />That's what I thought happened when I read that Sumatra moved 100 feet southeast (west?). I even looked up to see if Sumatra is south of the equator. <div class="Discussion_UserSignature"> </div>

 

[enkinight]

Maddad,<br /> You state that the earth has no large outside force acting upon the earth in concert with the earthquake....<br />Wouldn't the negative pressure (that is spaces' enviroment) be sufficient enough in slowing the rotation of the earth. My thinking being that this earthquake would have caused a bulge of mass because of the shift in mass, which in turn would cause more drag on the rotation via the increased static state that is strained by a larger equatorial bulge due to the redistribution mass knocked out of place. Which also affects the speed of the centrifuge motion?

 

[bobvanx]

I used Adobe Illustrator.<br /><br />One of the things I love to do is technical illustration.

 

[bobvanx]

>>large outside force acting upon the earth in concert with the earthquake<br /><br />I'll answer that.<br /><br />As far as we know, there are no large outside forces which couple with the Earth's tectonic plates. Some speculate that the Moon's tidal effect can initiate a quake.<br /><br />There is no "drag" to slow the Earth because there is nothing to drag against. The vacuum of space is pretty much perfectly slippery. The Earth's magnetic field does interact with the solar wind, but I don't thnk anyone has shown whether that would have any effect.<br /><br />Earth's rotation is pretty much governed by the Moon and by its own slow contraction as it cools and becomes more spherical.

 

[meteo]

The moon is retreating at 3.8cm/yr and the length of day is increasing by 0.23 microseconds per year. This is because of tidal forces.

 

[Maddad]

Enkinight<br />You now have enough information to work that out on your own.

 

[fossils]

http://www.jpl.nasa.gov/news/news.cfm?release=2005-009<br /><br />Alan Buis (818) 354-0474<br />Jet Propulsion Laboratory, Pasadena, Calif.<br /><br />Gretchen Cook-Anderson/Dolores Beasley (202) 358-0836/1753<br />NASA Headquarters, Washington, D.C.<br /><br />News Release: 2005-009 January 10, 2005<br /><br /><b>NASA Details Earthquake Affects on the Earth</b><br /> <br /><br />NASA scientists using data from the Indonesian earthquake calculated it affected Earth's rotation, decreased the length of day, slightly changed the planet's shape, and shifted the North Pole by centimeters. The earthquake that created the huge tsunami also changed the Earth's rotation.<br /><br />Dr. Richard Gross of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Dr. Benjamin Fong Chao, of NASA's Goddard Space Flight Center, Greenbelt, Md., said all earthquakes have some affect on Earth's rotation. It's just they are usually barely noticeable.<br /><br />"Any worldly event that involves the movement of mass affects the Earth's rotation, from seasonal weather down to driving a car," Chao said.<br /><br />Gross and Chao have been routinely calculating earthquakes' effects in changing the Earth's rotation in both length-of-day as well as changes in Earth's gravitational field. They also study changes in polar motion that is shifting the North Pole. The "mean North pole" was shifted by about 2.5 centimeters (1 inch) in the direction of 145 degrees East Longitude. This shift east is continuing a long-term seismic trend identified in previous studies.<br /><br />They also found the earthquake decreased the length of day by 2.68 microseconds. Physically this is like a spinning skater drawing arms closer to the body resulting in a faster spin. The quake also affected the Earth's shape. They found Earth's oblateness (flattening on the top and bulging at the equator) decrea

 

[mcbethcg]

That pretty much proves maddad wrong.<br /><br />Not that he'll ever admit it. Being a nursing student, he is much more qualified that Nasa scientists to judge these things.

 

[bobvanx]

No, no!<br /><br />If he ever admits he's wrong, it's the apocolypse! Seriously though, he has an out. These are all mathematically derived numbers, and the rotation change is below our threshold to measure. So he can disbelieve that the mathematical model is valid.

 

[meteo]

The polar motion change should be detectable.<br /><br />polar motion excitation X : -0.670 milliarcseconds<br />polar motion excitation Y: 0.475 milliarcseconds <br /><br />Measurements can be taken with and accuarcy of 0.05 milliacrseconds. I've been checking USGS every so often.

 

[Saiph]

You should give maddad a bit more credit. While he does stick to his guns he also knows when he's beat.<br /><br />And, I have to admit, he's usually correct anyway.<br /><br />He's also not one to dismiss mathematical calculations out of hand. He know's they're not iron clad, but if done well they give a good indication of even the most speculative areas. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[bobvanx]

>>You should give maddad a bit more credit<br /><br />Oh, I do, I think. When he sticks to information, he's great.<br /><br /><font color="orange">It's like a message forum, I'm here and you're not.</font>/safety_wrapper>