subaru, (the above) models predict that the earthquake should have affected rotation of the earth by shortening the length of a day by about three microseconds, or three millionths of a second. This happens because during the earthquake one of the tectonic plates (the India plate) subducted down beneath another plate (the Burma plate). The downward mass movement of the plate changed the earth's rotation just like a spinning ice skater bringing her arms closer to her body increases her rotation. When the earth spins faster, the days are shorter.

This rotation change is a prediction from a model, and the data [collected by ground- and space-based position sensors] is being analyzed to see if the predicted change actually occurred. The data comes in every day, but it will take a few weeks for the most accurate data to be received and analyzed.

The length of the day changes all the time in response to many different processes such as changes in the atmospheric winds or ocean currents. Changes in winds have by far the greatest effect on the length of the day: their effect is actually about 300 times larger than that predicted to be changed by this earthquake.

The earth wobbles as it rotates because its mass is not balanced about its rotation axis, just like a tire on a car will wobble as it rotates if the tire is not perfectly balanced. The size of the planet's wobble is usually about 33 feet. As the India plate subducted beneath the Burma plate, the mass of Earth was rearranged, not only causing the speed of rotation to change, which causes the length of the day to change, but also causing the wobbling motion of the planet to change by about an inch. The wobble is also affected by other influences, such as changes in atmospheric pressure.

I hope I have explained this clearly enough for you. Please do write back with further questions.

(Rated by 10 Council Members)

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.

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.

"Any worldly event that involves the movement of mass affects the Earth's rotation, from seasonal weather down to driving a car," Chao said.

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.

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) decreased by a small amount. It decreased about one part in 10 billion, continuing the trend of earthquakes making Earth less oblate.

To make a comparison about the mass that was shifted as a result of the earthquake, and how it affected the Earth, Chao compares it to the great Three-Gorge reservoir of China. If filled, the gorge would hold 40 cubic kilometers (10 trillion gallons) of water. That shift of mass would increase the length of day by only 0.06 microseconds and make the Earth only very slightly more round in the middle and flat on the top. It would shift the pole position by about two centimeters (0.8 inch).

The researchers concluded the Sumatra earthquake caused a length of day change too small to detect, but it can be calculated. It also caused an oblateness change barely detectable, and a pole shift large enough to be possibly identified. They hope to detect the length of day signal and pole shift when Earth rotation data from ground based and space-borne position sensors are reviewed.

The researchers used data from the Harvard University Centroid Moment Tensor database that catalogs large earthquakes. The data is calculated in a set of formulas, and the results are reported and updated on a NASA Web site.

The massive earthquake off the west coast of Indonesia on December 26, 2004, registered a magnitude of nine on the new "moment" scale (modified Richter scale) that indicates the size of earthquakes. It was the fourth largest earthquake in one hundred years and largest since the 1964 Prince William Sound, Alaska earthquake.

The devastating mega thrust earthquake occurred as a result of the India and Burma plates coming together. It was caused by the release of stresses that developed as the India plate slid beneath the overriding Burma plate. The fault dislocation, or earthquake, consisted of a downward sliding of one plate relative to the overlying plate. The net effect was a slightly more compact Earth. The India plate began its descent into the mantle at the Sunda trench that lies west of the earthquake's epicenter.

(Rated by 10 Council Members)

the earthquake should have affected rotation of the earth by shortening the length of a day by about three microseconds, or three millionths of a second.

during the earthquake one of the tectonic plates [the India plate] subducted down beneath another plate [the Burma plate]. The downward mass movement of the plate changed the earth's rotation just like a spinning ice skater bringing her arms closer to her body increases her rotation. When the earth spins faster, the days are shorter.

(Rated by 11 Council Members)

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.

The effects on the Earth's rotation from an earthquake even of this magnitude is much too small to be observed. The length of the day can be measured with an accuracy of about 20 microseconds and calculations of the source properties of the earthquake showed the change in the length of the day to be -2.676 microseconds, or in other words, less than can be effectively measured.

JPL has modeled the coseismic effect on the Earth's rotation of the December 26 earthquake in Indonesia by using the PREM model for the elastic properties of the Earth and the Harvard centroid-moment tensor solution for the source properties of the earthquake.

Since the length of the day can be measured with an accuracy of about 20 microseconds, this model predicts that the change in the length-of-day caused by the earthquake is much too small to be observed. And, since the location of the earthquake was near the equator, this model predicts that the change in polar motion excitation is also rather small, being about 0.82 milliarcsecond in amplitude. Such a small change in polar motion excitation will also be difficult to detect.

(Rated by 11 Council Members)

Here is more info for you. http://www.firstscience.com/SITE/AR…

(Rated by 11 Council Members)

(Rated by 11 Council Members)

Scientists have determined that this major shift in the Earth’s plates changed the planet’s shape – enough to shorten the day by fractions of a second and to shift the North Pole by an inch. The general shape of the Earth is slightly oblate – that is, it is not a perfect sphere but is slightly squished down, making it about 26 miles wider at the equator than between the poles. This shape, however, is not rigid, with climate being a major distorting force. But the magnitude nine earthquake last month almost certainly altered the shape as well. Recent calculations have estimated that this catastrophic land displacement caused a small reduction in the bulge, making the planet more round.

“The waistline was reduced by not quite a millimeter because of the earthquake,” said Benjamin Fong Chao from NASA’s Goddard Space Flight Center.

This slimming down sped up the rotation of the Earth, much like when a spinning ice skater pulls in her arms to increase her speed. The length of the day correspondingly decreased by 2.68 millionths of a second.

Also check these links for more details: http://earthobservatory.nasa.gov/Ne…

http://www.theage.com.au/articles/2…

http://www.physorg.com/news2622.htm…

http://www.rediff.com/news/2005/jan…

(Rated by 11 Council Members)

There was an interesting article on the web about it recently. Here is what it says:

In covering the massive, tsunami-generating earthquake off the northwest coast of Sumatra this weekend, many news outlets picked up a statement from Enzo Boschi, head of Italy's National Institute of Geophysics, saying the temblor was strong enough to disturb the Earth's rotation. Can an earthquake really affect the way the planet spins on its axis?

Yep. As you'll recall from science class, the rotating Earth resembles a spinning top: The planet's axis does not always point in exactly the same direction but wobbles very slightly, describing small but measurable circles at the poles. A very large earthquake—one of a magnitude of 9.0 or greater—can shift enough mass relative to that of the entire Earth to alter, very minutely, the course of that wobble. But the planet's speed of rotation (which, of course, determines the lengths of our days) remains unchanged, so we don't need to worry about adjusting our watches.

In this case, the 9.0-magnitude shock was a "megathrust" quake, which occurs where one tectonic plate is forced beneath another. Initial U.S. Geological Survey data from the quake and its dozens of powerful aftershocks indicate that some 740 miles of the boundary between the India plate and the Burma plate slipped an average of 15 meters and that the sea floor thrust up several meters. It is difficult to determine the total mass of the crust that shifted because the movement was irregular, but when so much of the Earth moves so far, the wobble of its axis will jog slightly, too.

Geophysicists have still not calculated the exact effect of this earthquake on the wobble, but they will as data from the quake and aftershocks are plugged into complex mathematical models developed for that purpose in the 1950s and early '60s. Wobble was a hot topic back then because a series of powerful megathrust quakes—the 9.0 Kamchatka quake in 1952, the 9.1 Andreanof Islands quake in 1957, the 9.5 Chile quake in 1960, and the 9.2 Prince William Sound quake in 1964—provided a lot of data to work with. (source: http://slate.msn.com/id/2111443/…)

Here are some other interesting sites you can have a look at: tokyo.usembassy.gov/e/p/tp-20050113-04.html business-times.asia1.com.sg/story/0,4567,141747,00.html www.surfersvillage.com/news.asp?Id_…

Hope this helps. Best of luck.

(Rated by 10 Council Members)

(Rated by 11 Council Members)

One such scientist Richard Gross, who is a a geophysicist at the US space agency's Jet Propulsion Laboratory in California, believes a shift of mass toward the Earth's centre during the eathquake caused the earth to spin faster by three microseconds and tilt about one inch on its axis.

The Earth's poles travel a circular path that normally varies by about 33ft, so an added wobble of this scale is unlikely to cause long-term effects.

Dr. Gross says, "That continual motion is just used to changing, the rotation is not actually that precise. The Earth does slow down and change its rate of rotation."

Scientists have long theorised that changes on the Earth's surface such as tide and groundwater shifts and weather could affect its spin, but they have not had the measurements to prove it.

Seismologist, Hiroo Kanamori from the California Institute of Technology says, "Even for a very large event, the effect is very small, it is very difficult to change the rotation rate substantially".

Hope this is helpful somewhat in answering youer query.

Source: http://news.bbc.co.uk/1/hi/sci/tech…

(Rated by 11 Council Members)

Source: www.scientificamerican.com…

Models predict that the earthquake should have affected rotation of the earth by shortening the length of a day by about three microseconds, or three millionths of a second. This happens because during the earthquake one of the tectonic plates [the India plate] subducted down beneath another plate [the Burma plate]. The downward mass movement of the plate changed the earth's rotation just like a spinning ice skater bringing her arms closer to her body increases her rotation. When the earth spins faster, the days are shorter. Is this change permanent? The length of the day changes all the time in response to many different processes such as changes in the atmospheric winds or ocean currents. Changes in winds have by far the greatest effect on the length of the day: their effect is actually about 300 times larger than that predicted to be changed by this earthquake.

Hope this answers your query. Good luck !

(Rated by 10 Council Members)

In general, any mass shift, such as that accompanying the Indonesian earthquake, will cause both the length of the day to change and the Earth to wobble. None of these changes affect the Earth's orbit, they only affect its rotation," says Gross.A tsunami is just an ocean wave with very little mass motion involved, the tsunami itself would not have had much of an effect on the Earth's rotation, either on the length of the day, or on the wobble. So for now at least, while the Earth might be rotating 3 millionth of a second faster and wobbling more on its axis, it is definitely not Armageddon yet.

(Rated by 10 Council Members)