The 8.9-magnitude earthquake in Japan on March 11 shortened Earth’s day by 1.8 millionths of a second, according to NASA scientists. Earth still tilts on its axis by 23.5 degrees, as before. But, since the March 11 earthquake, Earth spins faster than before, and our day is ever so slightly shorter from sunrise to sunset.
This change is so small that sophisticated instruments cannot detect it. Instead, a team of scientists at NASA’s Jet Propulsion Laboratory calculated the change in Earth’s rate of spin, using computers and earthquake data.
EarthSky’s Beth Lebwohl spoke to Richard S. Gross, the team’s leader and a senior scientist at NASA’s Jet Propulsion Laboratory. His group used seismic data showing the amount of slippage in the fault line necessary to create the Japan earthquake, in order to calculate the shift in mass inside Earth and subsequent change in Earth’s rate of spin.
This is just like a spinning ice skater. As she moves her arms closer to her body, she spins faster. The Earth is similar to that. If the mass of the Earth moves closer to its rotation axis, the planet will spin faster.
Overall, Earth’s axis of rotation is tilted at an angle of 23.5 degrees relative to the orbital plane at which Earth travels around the sun. This tilt causes our four seasons, and this tilt has not changed. What has changed is the orientation of the solid Earth with respect to our planet’s tilt. In other words, the earthquake rearranged Earth’s mass, bringing more mass a bit closer to the Earth’s rotation axis, causing the Earth to rotate slightly faster and the length of the day to shorten.
This change doesn’t effect the (degree) of tilt of the axis of Earth in space, or the orbit of the Earth around the sun. The only way Earth’s tilt or orbit can be affected is if some external force – like an asteroid – hits the Earth. These are internal processes – earthquakes or winds or currents. They can only change how the Earth’s mass is balanced. The Earth is a big massive rotating body. Anything that is reasonable to happen is going to cause only a very small change. Earth really is a very stable system.
Dr. Gross told EarthSky that – while a shift in Earth’s axis and rotational speed might sound striking, perhaps even scary – Earth is shifting slightly all the time, owing mostly to atmospheric and ocean currents.
It’s a perfectly natural motion of the Earth, and the biggest cause of this motion are changes in the atmospheric winds, and changes in the ocean currents. The winds and the currents carry a lot of energy with them, and that energy can be exchanged with the solid Earth to cause Earth’s rotation to change.
If you were to stop the winds completely, Dr. Gross said, you would change the length of Earth’s day by about 4 milliseconds. He added that other earthquakes have also shifted Earth’s axis, for example, the February 2010 earthquake in Chile and an even stronger earthquake in Chile in 1960.
The largest earthquake that has happened in Earth’s recorded history was the 1960 earthquake in Chile. I did the same calculations for that earthquake (as for the 2011 Japan earthquake and 2010 Chile earthquake), and, according to my calculations, the 1960 earthquake should have shortened the length of the day by 8 microseconds.
Chile earthquake might have shortened Earth’s day, but how?
He explained that his figures on the shifting caused by Japan’s earthquake are preliminary. His team is still working on the calculations.
We’re looking at the observations right now to see if these predicted effects are actually observable, but it will take some time for us to reduce the data – that is, to reduce the effects of the atmosphere and oceans – to see the much smaller effects caused by the earthquake. But if we’re successful, this will be the first time that we’ll see a verified effect of the earthquake on the Earth’s rotation.
The magnitude-8.9 earthquake that struck northern Japan on Friday not only changed the balance of the planet and altered Earth’s spin. It also moved the coastline of the island nation of Japan. Global positioning stations closest to the earthquake’s epicenter jumped eastward by up to 13 feet. In the meantime, our day has gotten shorter by 1.8 millionths of a second.
Why then, do we find the earth’s axis wobbles?
Chandler wobbleFrom Wikipedia, the free encyclopediaJump to: navigation, search
The Chandler wobble is a small motion in the Earth’s axis of rotation relative to the Earth’s surface, which was discovered by American astronomer Seth Carlo Chandler in 1891. It amounts to 20 feet (9 meters) on the Earth’s surface and has a period of 433 days. This wobble combines with another wobble with a period of one year so that the total polar motion varies with a period of about 7 years. The Chandler wobble is an example of the kind of motion that can occur for a spinning object that is not a sphere; this is called a free nutation. Somewhat confusingly, the direction of the Earth’s spin axis relative to the stars also varies with different periods, and these motions (caused by the tidal attraction of the Moon and Sun) are also called nutations, except for the slowest, which is the precession of the equinoxes.
The existence of a free nutation of the Earth was predicted by Isaac Newton in Corollaries 20 to 22 of Proposition 66, Book 1 of the Philosophiæ Naturalis Principia Mathematica, and by Leonhard Euler in 1755 as part of his studies of the dynamics of rotating bodies. Based on the known flattening of the Earth he predicted that it would have a period of 305 days. Several astronomers searched for motions with this period, but none were found. Chandler’s contribution was to look for motions at any possible period; once the Chandler wobble was observed, the difference between its period and the one predicted by Euler was explained (by Simon Newcomb) as being caused by the non-rigidity of the Earth. The full explanation for the period also involves the fluid nature of the Earth’s core and oceans: the wobble in fact produces a very small ocean tide with an amplitude of c. 6 mm, the pole tide, which is the only tide not caused by extraterrestrial bodies. Despite the small amplitude, the gravitational effect of the pole tide is easily detected by the superconducting gravimeter (see e.g. Fig. 2.3 in Virtanen 2006).[1]
To measure the wobble, the International Latitude Observatories were established in 1899. (The wobble is also called the variation of latitude.) These provided data on the Chandler and annual wobble for most of the 20th century, though they were eventually superseded by other methods of measurement. Monitoring of the polar motion is now done by the International Earth Rotation Service.
The wobble’s amplitude has varied since its discovery, reaching its largest size in 1910 and fluctuating noticeably from one decade to another. While it has to be maintained by changes in the mass distribution or angular momentum of the Earth’s outer core, atmosphere, oceans, or crust (from earthquakes), for a long time the actual source was unclear, since no available motions seemed to be coherent with what was driving the wobble.
Richard Gross (2001) of the Jet Propulsion Laboratory, California, used computer simulations to discover the source of the Chandler Wobble. Gross found that two thirds of the ‘wobble’ was caused by fluctuating pressure on the sea bottom due to temperature and salinity changes and wind-driven changes in the circulation of the oceans. The remaining third is due to atmospheric fluctuations [2]
Also, other reports say the axis shifted as much as 6.5 inches!
The world’s fifth-largest, 8.9 magnitude quake was caused when the Pacific tectonic plate dove under the North American plate, which shifted Eastern Japan towards North America by about 13 feet (see NASA’s before and after photos at right). The quake also shifted the earth’s axis by 6.5 inches, shortened the day by 1.6 microseconds, and sank Japan downward by about two feet. As Japan’s eastern coastline sunk, the tsunami’s waves rolled in
I understand that the rotation speed of the Earth has increased by 1.8 microseconds and the tilt angle has not changed any measurable amount. Has the relative position of the Earth within the universe changed at all? For instance, is the universe expanding or contracting slightly more or less by this event beyond an Earth wobble?
The position of Earth does not change when you sit on your barstool, Norm.
Norm – not only has the tilt angle not changed by any measurable amount, but also the rotation speed of the earth has not changed by any measurable amount. What is being presented as fact after every major earthquake is not fact at all, but is the output of a physical model. In other words the 1.8 microsecond figure is synthetic and is not guaranteed to be an accurate reflection of reality. It is an attempt to quantify how the rotation of the Earth MAY HAVE been affected by the earthquake and not a fact demonstrated by any observation.
William, absolutely correct.
No guarantee of reality about this research.
Of course, the same could be said for nearly all of astronomy … and yet the picture presented to us by astronomers forms our cosmology … our picture of the universe we live in.
It’s interesting to think about, isn’t it?
Best,
Deborah
I stopped sitting on barstools. Too much science to observe. I agree that it isn’t science unless it is observable and repeatable. The scientific method rules! Perhaps if one were to measure the GPS positions or interferometer readings or other similar, appropriate measurements with a great deal of accuracy and precision, they will have returned to the same original position after a brief preturbation. Of course we won’t KNOW that without taking the data, right?
After japan’s earth quake we noticed that our PC (CRT) Monitor showing colour patches if we face the monitor in North or East direction. My question is does any changes came in Earth Magmatic field after this Quake?
Pradip Das
India Shillong Meghalaya
East Khasi Hills
C/o computer world
+919774001980.
Pradip, at this writing, I have not seen any data related to Earth’s magnetic field and the March 11 earthquake. Perhaps someone else has seen these data.
Thank you for visiting,
Deborah
dear mam BYRD, what is good for mother earth the faster or the slower,and what happen to our country in Philippines,
Genelita,
No one can predict the future.
Events like earthquakes are natural for Earth, but our human population has grown very large. So the effects on humans can be difficult, or even devastating.
It is good to be prepared for earthquakes, if you live in an earthquake-prone region.
Take care and all the best,
Deborah
So the earth is on a 23deg tilt towards the Sun, I take it that the sun is WHAT? Straight at 90deg by Whose calculations? and Where is The suns Measuring point taken from/other than its own.
Does the Sun tilt? move about ?
Solar Flares, the constant Nuclear Forces within our Dear old sun Doesn’t alter its Mass?Make it wobble? Grow in size?(the Sun is in its Half Life so scientists say)
Am I correct in saying we Have a similar movement of Force going on in the Core of the Earth,too? Will or Does this not affect Earths Stability or is it not of concern?
Seems there is a lot of VOLCANO activity about Lately.
Mother Nature I see.. Lest we Forget.. about The Hidden Forces she Does possess.
Maybe Perfect paranoia is Perfect awareness for some, I still ask Why we USED the Pacific for Numerous ATOMIC Mega Tonne Explosive Testing.
The Eggshell Theory.
The tilt is measured as an angle between the Earth axis the plane in which the center of mass of the Earth moves in its elliptical orbit around the sun. But of course this plane of motion is only relative to the sun, since the the solar system itself is swirling about the galaxy and the galaxy is moving out from the big bang among other motions.
That should read the tilt is the angle between the Earth axis and a line perpendicular to the plane of motion of the center of mass of the Earth in its elliptical orbit around the sun.
Just asking, with all those strong earthquakes since the 1900, Can we say now that a day is 23 hours 59 min. and 59.999 seconds ? Or whats the correct approx. numbers for it ?
Interesting read. Thanks for the information. It’s very helpful…
[...] earthquake in Japan shortened the day by 1.8 millionths of a [...]
Thank you for the information.
My question: So when the news reports said that the earth’s axis shifted by 6.5 inches they meant the effective mass of the Earth has shifted by that amount?
CSP, Earth’s mass has shifted, yes. it’s like an ice skater pulling in her arms to rotate faster. The mass has shifted ever so slightly toward Earth’s rotation axis, causing Earth’s spin to be ever so slightly faster.
so,the axial tilt changed,or the earth shifted from its rotational axis,or both??
The axial tilt did not change. Mass – stuff – inside Earth moved closer to the axis of rotation. So Earth is spinning slightly faster now. Like the ice skater pulling in her arms …
So where where does the online media get that information about the earth’s axis tilting?
I see it everywhere but no links to any research… can they just throw out claims like that?
Well, this concept is a difficult one. EarthSky had written about it previously – when Richard Gross made a similar calculation – and I recall that we struggled with presenting the concept correctly.
Most media probably talked to Dr. Gross. Scientists themselves also have to struggle to explain things …
Deborah
After the earthquake the earth spins a 1.8 millioneth of a second faster, How does it effect the climate of future prospectus.
according to me, wedn’t need pay more attention to 1.8 millionneth of second, but what is the biggest effected by japans mega earthquake. the scientist has to predicted movement of earth plate, and more focus to closer areas to japan. it’s like Philipines small earth plate.
AMREY ATJEH- SUMATERA island