Earthquake Disturbs Planetary Rotation???

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MetMan

Well-Known Member
"All the planet is vibrating" from the quake, said Enzo Boschi, the head of Italy's National Geophysics Institute. Speaking on SKY TG24 TV, Boschi said the quake even disturbed the Earth's rotation.

Can any earth scientists out there explain this? Did the quake change the earth's moment of inertia enough to make a measurable change in rotation rate?

I find that very difficult to believe.

The earthquakes did not change the mass of the planet, nor could they have possibly changed the distribution of mass (and therefore the center of mass) significantly enough to alter the rotation of the planet.

I'm no planetary geologist or anything, but that just seems nearly physically impossible. Especially the nature of the release of energy that an earthquake is.

QUICK!!!

Somebody call Bruce Willis!

Everybody! Go flush your toilets! Make sure the water rotates clockwise!

OK, a little googling has resulted in the following numbers:

A 9.0 on the Richter scale is equivalent to 32*10^9 tons of TNT or 32,000 megatons. That's a lot of energy!

The rotational kinetic energy of the earth is reported on various sites as between 2 and 4*10^29 joules.

32, 000 megatons is 1.3*10^20 joules.

So the sesimic energy is still less than one-one billionth of the total kinetic energy. Seems like it would take pretty sensitive instruments to measure the change.

Neat stuff though. One discussion talked about finding a way to bleed off the earth's rotation to generate electricity!

Good stuff but remember the earths seismic activity as greatly decreased since the formation of the crust. I can't believe there are insturments out there that could record such a miniscule rotational change if there were one.

Sandman, the flush rotation will only change when the poles reverse again Now that should be interesting.... North south and South north Tee hee

As long as the toilet water continues to go down on flush rather then spitting back up at me either clockwise or counterclockwise is cool with me

Andy

Originally posted by Micromeister
Good stuff but remember the earths seismic activity as greatly decreased since the formation of the crust.

It is my understanding that "seismic activity" *is* activity of the earth's crust. Generally speaking anyway. In fact, "seismic activity" is defined as "the phenomenon of Earth movements." These movements take place within, and are measured within, the crust.

I can't believe there are insturments out there that could record such a miniscule rotational change if there were one.

two things: atomic clocks and positional astronomy

Originally posted by MetMan
"All the planet is vibrating" from the quake, said Enzo Boschi, the head of Italy's National Geophysics Institute. Speaking on SKY TG24 TV, Boschi said the quake even disturbed the Earth's rotation.

Can any earth scientists out there explain this? Did the quake change the earth's moment of inertia enough to make a measurable change in rotation rate?

Disturbed, not disrupted.

The earth is a rotating viscous fluid body. A vibration in such a body can be translated transverse vibrations to angular vibration. As the earth "rings" from the seismic shocks, some of that ring can turn into a periodic (wave-like) speeding and slowing of its rotation. Check out the videos of shuttle astronauts playing with globules of water and see how they act when poked. Bulges don't just boing in and out. They boing in and out around in circles.

It'll settle down to how it was before. Chances are this happens often. We're just recently able to measure it with the accuracy needed to detect it.

Originally posted by DynaSoar
The earth is a rotating viscous fluid body. A vibration in such a body can be translated transverse vibrations to angular vibration. As the earth "rings" from the seismic shocks, some of that ring can turn into a periodic (wave-like) speeding and slowing of its rotation.

And thanks to the principle of conservation of angular momentum, we at TRF can actually make the earth speed up if we all agree to jump up at the same instant! The temporary decrease in mass will result in an increase in angular velocity.

Likewise, a gigantic bulge of water can cause the planet to slow, much like Dorothy Hamill extending her arms in a spin.

Originally posted by MetMan
Likewise, a gigantic bulge of water can cause the planet to slow, much like Dorothy Hamill extending her arms in a spin.

Maybe if Drew Carrey tried a spin...

Originally posted by DynaSoar
Chances are this happens often. We're just recently able to measure it with the accuracy needed to detect it.

It happens all the time. This earthquake, magnitude 9.0, was one of the four largest quakes since 1900, so its effect was much greater than that of most earthquakes. And so its effects are easier to measure, plus the instruments are more sensitive than they used to be.

With all of the GPS satellites out there, outside of the effects of the miniscule change in rotational rate (which is now being widely reported as a possibility), this could potentially wreak havoc on the programming of the satellites and/or the receivers.

As I recall, the satellites operate on a principle of differential signal reception. If the rate of rotation has indeed been affected, they'll have to reposition the satellites in orbit to match the new rotational rate (a fairly easy thing to do once the calculations are made). But more significantly, they'll have to update the internal calculations made by each and every GPS device that uses the newly repositioned satellites.

The alternative is to leave the devices as they are, and just release new devices in the next few years and make consumers buy all new devices or else face gradually degrading accuracy in the years to come.

WW

that's not how GPS works. the relative positions of the satellites are known very precisely, you don't want to mess with that. anyways the change in rotation would be orders of magnitude less than the ultimate resolution of GPS.

in a couple weeks we'll hear from the positional astronomers, how much the earth's rotation changed. I bet it will be a microsecond or smaller.

What I have read is that the Northern tip of Sumatra could have moved as far as 36 meters south west of where it was before. So, if you burried something in Sumatra and were counting on GPS to get you back to that spot, you're going to be about 36 meters (118 feet) off. Or, it could have moved that much vertically, or some combination.

That much energy might change the earth's rotation, but only a very tiny bit (10^-8 second or there about?).

Most of the mass of the earth is molten and free-flowing anyway. I hardly think a tiny scootch of the earth's very thin crust would have a lot of effect compared to the convection already occuring in the interior of the planet.

urbanek

I'm no seismologist, but wouldn't it be like throwing a rock into the water. It disturbs the water temporarily with a ripple effect, but eventually settles back down to calm. The rock itself has really no overall effect on the body of water itself.
A 9.0 quake realeases alot of energy that potentially may cause a 'ripple' in the earths rotation but would only be for a moment as the earth settles back into it's normal rotation. Not a scientific explanation, but does that make sense?

I had originally thought that the water wave had caused the change in the mass distribution, but it's actually the slab of crust that slid further into the earth under water that caused the rotation rate to speed up.

Angular momentum is conservative, so with a lot of mass far away from the axis of rotation, the earth spins at a certain rate (once per day). When you move mass inward, the earth speeds up to maintain the same angular momentum. Think of the figure skater analogy.

The change in rotation period that I heard quoted was on the order of microseconds.

You can actually demonstrate this in a classroom if you have an office chair that spins easily. It take a strong stomach, though!

i have heard that maps of the earth must be redrawn because they are now off in several parts of the region. thats pretty cool.

it hasnt affected my alignment on my telescope, but i dont have extremely precise instrumentation. im guessing that a substatial change in the rotation wouldnt be noticed by the naked eye for a couple thousand, if not million years.

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