From NASA’s Jet Propulsion Lab: The March 11, magnitude 9.0 earthquake in Japan may have shortened the length of each Earth day and shifted its axis. But don’t worry-you won’t notice the difference.
Using a United States Geological Survey estimate for how the fault responsible for the earthquake slipped, research scientist Richard Gross of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., applied a complex model to perform a preliminary theoretical calculation of how the Japan earthquake-the fifth largest since 1900-affected Earth’s rotation. His calculations indicate that by changing the distribution of Earth’s mass, the Japanese earthquake should have caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second).
The calculations also show the Japan quake should have shifted the position of Earth’s figure axis (the axis about which Earth’s mass is balanced) by about 17 centimeters (6.5 inches), towards 133 degrees east longitude. Earth’s figure axis should not be confused with its north-south axis; they are offset by about 10 meters (about 33 feet). This shift in Earth’s figure axis will cause Earth to wobble a bit differently as it rotates, but it will not cause a shift of Earth’s axis in space-only external forces such as the gravitational attraction of the sun, moon and planets can do that.
Both calculations will likely change as data on the quake are further refined.
In comparison, following last year’s magnitude 8.8 earthquake in Chile, Gross estimated the Chile quake should have shortened the length of day by about 1.26 microseconds and shifted Earth’s figure axis by about 8 centimeters (3 inches). A similar calculation performed after the 2004 magnitude 9.1 Sumatran earthquake revealed it should have shortened the length of day by 6.8 microseconds and shifted Earth’s figure axis by about 7 centimeters, or 2.76 inches. How an individual earthquake affects Earth’s rotation depends on its size (magnitude), location and the details of how the fault slipped.
Gross said that, in theory, anything that redistributes Earth’s mass will change Earth’s rotation.
“Earth’s rotation changes all the time as a result of not only earthquakes, but also the much larger effects of changes in atmospheric winds and oceanic currents,” he said. “Over the course of a year, the length of the day increases and decreases by about a millisecond, or about 550 times larger than the change caused by the Japanese earthquake. The position of Earth’s figure axis also changes all the time, by about 1 meter (3.3 feet) over the course of a year, or about six times more than the change that should have been caused by the Japan quake.”
Gross said that while we can measure the effects of the atmosphere and ocean on Earth’s rotation, the effects of earthquakes, at least up until now, have been too small to measure. The computed change in the length of day caused by earthquakes is much smaller than the accuracy with which scientists can currently measure changes in the length of the day. However, since the position of the figure axis can be measured to an accuracy of about 5 centimeters (2 inches), the estimated 17-centimeter shift in the figure axis from the Japan quake may actually be large enough to observe if scientists can adequately remove the larger effects of the atmosphere and ocean from the Earth rotation measurements. He and other scientists will be investigating this as more data become available.
Gross said the changes in Earth’s rotation and figure axis caused by earthquakes should not have any impacts on our daily lives. “These changes in Earth’s rotation are perfectly natural and happen all the time,” he said. “People shouldn’t worry about them.”
So, plate tectonics can change the climate? And melting ice causes plates to move, causing earthquakes – meaning plate movement? I think I’ve solved all of our problems: Move something of weight equal to that of melting ice to Greenland. So, Al Gore really can save the planet!
Interesting—and not a word about ‘climate change’. Bravo!
/Mr Lynn
Well, the silver lining is that Obama’s term will be about 4 ms shorter.
Gross is as sharp as a tack on LOD problems, but for any who are wondering about the mechanism, I hope this helps. Hot mantle slowly rises, and cools, then sinks, but not smoothly. Over the long haul the lithosphere’s moment of inertia doesn’t change, but when a cooled mass drops suddenly, and is replaced by warmer mass of less density, rotational inertia decreases and the earth speeds up, until the sunken mass warms and the replacement mass cools. So it has to do with uneven cooling and flow of the mantle. Think of big kids and little kids on the merry-go-round switching places from the inside to the outside.
True, this is so far an academic excercise, but it has its raison d’etre in the new science of satellite measured earth rotation, which has thrown lots of light on earth processes. And the time may come when even microseconds can be measured, which would correspond to half a millimeter at the equator, measured instantaneously.
What about:
“These changes in Earth’s climate are perfectly natural and happen all the time. People shouldn’t worry about them.”
Rod says:
March 17, 2011 at 6:29 am
Changes in the length of day mean changes in earth’s rotation and thus its angular momentum.
No, in its moment of inertia. Think of a spinning ice skater. She has a certain [fixed] angular momentum. If she stretches out her arms, she increases her moment of inertia, and since the angular momentum is not changed her spin must slow down.
I would think that if the center of mass of the Earth has shifted, so too have the orbits of the satellites that encircle us, including the GPS birdcage. The entire reference frame has shifted along with everything in it. If so this will have interesting effects in chaotic systems. At least our projections from our models will be impacted because we now have new parameters injected into the system. The butterfly’s wing beats in Paraguay and something happens somewhere, but what? Where?
MAY? Heh
@steveta_uk says:
March 17, 2011 at 3:32 am
Every morning, lots of people commute into cities, and every evening they go home again. As a result, city centres will gain the mass of many people, cars, and other stuff, and so get heavier, and flex downwards, then revert in the evening. Since this is cyclic, the cities may start to oscillate up and down in a 24-hour rhythm. If some city somewhere happens to have an 11.574 uHz resonant frequency (that’s 24 hrs), this could be catastrophic!
Has anyone at NASA looked into this yet?
————-
REPLY
Interestingly, the World Wildlife Federation’s latest report on sustainable energy mentions that the vibrations of city centers might be harnessed for electrical generation!
http://wwf.panda.org/what_we_do/footprint/climate_carbon_energy/energy_solutions/renewable_energy/sustainable_energy_report/
I humbly offer this great work of fiction for Anthony, readers & mods of WUWT!
Leif Svalgaard says:
March 17, 2011 at 8:04 am
No, in its moment of inertia. Think of a spinning ice skater. She has a certain [fixed] angular momentum. If she stretches out her arms, she increases her moment of inertia, and since the angular momentum is not changed her spin must slow down.
Leif Svalgaard says:
March 17, 2011 at 8:04 am
No, in its moment of inertia. Think of a spinning ice skater. She has a certain [fixed] angular momentum. If she stretches out her arms, she increases her moment of inertia, and since the angular momentum is not changed her spin must slow down.
Thanks. You are right. What I am seeking to understand are changes in vorticity within the atmosphere when earth’s rotation speed changes.
Mark Wagner says:
why did all the reported shifts work to shorten the days? coincidence? would not some seismic events work to lengthen days as well?
Exactly what I was wondering. Anyone have an answer?
“The March 11, magnitude 9.0 earthquake in Japan may have shortened the length of each Earth day … ”
Swell! As if there was too much time in the day already. Add that to the hour lost last Sunday. We need to start saving time if only for our children.
Mark Wagner at 521, Tony G at 932: Volcanic activity has the opposite and steadier effect of slowing the earth down. Hot magma arrives at the surface allowing the older and cooler surface to sink. This is a microcosm of large scale mantle convection. Lateral fault movements have no effect on LOD, and uplift of cold rock, while common on the continents, runs against the grain in the mantle. Slow rising of hot mantle slows the earth down. I suppose the interface between tectonic plates is smoother than that between the top plate and the continents, leading to upward movement of hot lower plates being smoother than downward moving upper plates. So bigger, deeper quakes typically involve a loss of inertia, which loss is balanced out by the steadier rise of the lower plates. If you want a better answer you can contact Gross at NASA.
I’ll have to modify that. Whereas the rise and fall of masses is simultaneous, the cooling is steady, and the process of cooling leads to contraction, a T inversion, and the ensuing convection leading to quakes. Forget about plate roughness.
I call bull-crap!!!
by Alan the Brit
So, he is telling us that the measured shift amounts to diddly-squat when all is taken into account – why did he bother?
—————————————-;
It was a model prediction – it was not a measurement. Until it’s confirmed by measurement it’s fiction.
The season change in the LOD is on the order of millisecs when compared to UTC.
by TFN Johnson says:
March 17, 2011 at 2:16 am
Slowing the Earth’s rotation causes the moon to move away a little bit, in order to preserve angular momentum of the whole Earth/Moon system.
——————-;
To first order, it’s actually a 3 body graviation problem since you can’t ignore the Sun.
The LOD of the Earth will continue to decrease and the Moon’s LOD will continue to continue to increase as the Moon continues to move away from the Earth since the Earth and the Moon are gravitionally phased locked.
Interestingly, Poincare demostrated over 100 years ago the 3 body gravitation problem was chaotic (which until recently – with the exception of Einstein, has been largely ignored.)
“The LOD of the Earth will continue to decrease and the Moon’s LOD will continue to continue to increase as the Moon continues to move away from the Earth since the Earth and the Moon are gravitionally phased locked.”
Ahh, the rotation of the Moon will speed up as the rotation of the Earth slows down. Sometime after the Sun becomes a Red Drawf, the speeds will be the same.
The Earth’s axis has long had a considerable tilt. Now I fear it is bent too.
Is this just more media science ? Media science is good for funding.
It’s ok because the melting of the last ice age surely lowered lots of formerly elevated water, increasing the speed of rotation. We’re just making up for that a little.
The magnetic pole is shifting. The tectonic plate will adjust accordingly. Expect more big earthquakes as the magnetic pole move toward Siberia.
When grounded polar ice melts the earth slows down, leaving the ground depressed. As the ground rebounds, the earth speeds back up, but at present not enough to make up for tidal acceleration (2.3ms/century less .6ms/century as I recall). As the relative masses of the earth, moon, and sun are easily obtained through Newtonian physics, and as the absolute distances may be measured by triangulation or calculated by measurement of the gravitational constant, so may the relative tidal contributions of the moon and sun be calculated precisely. And since the growing distance to the moon can now be measured by laser ranging, its growing angular momentum can be calculated, hence the earth’s loss of angular momentum due to lunar, then solar tides. This calculated loss is then compared to observed loss as obtained through ancient astronomical observations and modern telescopic sighting and satellite telemetry, and the long term difference is attributed to glacial isostatic adjustment. Then the considerable fortnightly contribution of zonal tides may be modeled and deducted from measured LOD, leaving seasonal variation to be accounted for, most of which may be explained by atmospheric coupling. Other components include groundwater depletion, terminal lake depletion (mainly the Caspian and Dead Sea) opposite artificial reservoirs, ocean basin adjustment to changing sea levels and other activity of the lithosphere, etc.
After all this we are left to argue whether remaining trends are due to core mantle coupling, ice growth in Antarctica, less sea level rise than claimed, and so on. At least LOD places limits on estimations of current rate of sea level rise.
JudyW says:
March 17, 2011 at 6:00 pm
The magnetic pole is shifting. The tectonic plate will adjust accordingly. Expect more big earthquakes as the magnetic pole move toward Siberia.
No, the magnetic field is generated deep in the core and has nothing to do with the plates.