Japan quake causes day to get shorter

[Dreamsphere]

PhysOrg Mobile: Japan quake causes day to get a wee bit shorter

Could this have implications for sensitive ground based astronomical instruments?

[Struders]

really? I cant figure out why it would have that effect. Isn't it like sanding on a boat and blowing the sails to move? quote "for every action there is an equal and opposite reaction"?

I am probably wrong though, I just don't get the physics behind this one.. (someone prove me wrong )

[RogerTheDodger]

Could be like an ice skater pulling their arms in whilst in a spin, it causes the body to spin faster... if the plate went deeper then that could be it.

[Capricorn]

What if the other plate that was stopping it going down moved up. That would mean that the surface was higher so we spin slower.

So the spinning skater theory works both ways.

Anyway the earth has been slowing down very slowly for millions of years. Didn't it start out with something like a 5 hour day?

[brianb]

I just don't get the physics behind this one..

If the plates were in isostatic balance before and after, but the denser plate moved lower, conservation of angular momentum would cause an increase in spin speed.

We're not talking much here, a change in the day length of a few microseconds .... if you have a very good clock and an accurate transit instrument, you might be able to see the difference after a few weeks. But it's likely that other earth movements will have happened before then to even things out. Large earthquakes happen when movement "freezes" then releases suddenly - in this case, a movement of 90 mm per year has accumulated over many decades & then jumped several metres.

[Stephen]

via Prof Brian on Twitter :

Entire Japan coast shifted 2.4 metres, earth axis moved ten inches and days shortened by 1.26 microseconds

[bcfc1979]

yep the earth the started with a 5 hour day, but our moon gradually slowed us down.... god bless the disco chan

[Dreamsphere]

... but the Moon was formed from the Earth following a collision with anotjer planetary body so can only have played a part after that point in time.

yep the earth the started with a 5 hour day, but our moon gradually slowed us down.... god bless the disco chan

[wpitcairn]

I think there may be bigger problems regarding the fallout from the explosions at the Nuclear plants.

[acey]

I'm very surprised by this but Gross seems to have done a lot of work on it.

All Days Are Not Created Equal - NASA Jet Propulsion Laboratory

By comparison, the lengthening of Earth's day due to tidal friction is only about 2 milliseconds per century.

Tidal acceleration - Wikipedia, the free encyclopedia

These are the references for his most recent papers:

Gross, R. S., Earth rotation variations — long period (invited), in Physical Geodesy, edited by T. A.

Herring, submitted, Treatise on Geophysics vol. 11, Elsevier, Amsterdam, 2005.

Gross, R. S., and B. F. Chao, The rotational and gravitational signature of the December 26, 2004

Sumatran earthquake (invited), Surv. Geophs., submitted, 2005.

[Dreamsphere]

From BBC News - Japan quake: Fears of second nuclear reactor blast the Japanese authorities are playing down the risk of a nuclear leak. So far the leak has been very small as the explosion only affected the perimeter building and wasn't nuclear in nature, I suppose in truth, no one can actually say for sure what might happen as they are still suffering aftershocks and haven't been able to access the facility properly to assess the extent of the damage.

"There is a risk of a second explosion at the quake-hit Fukushima power station, Japanese officials have said.

However, chief cabinet secretary Yukio Edano said the facility could withstand the impact and the nuclear reactor itself would not be damaged."

I think there may be bigger problems regarding the fallout from the explosions at the Nuclear plants.

[brianb]

chief cabinet secretary Yukio Edano said the facility could withstand the impact and the nuclear reactor itself would not be damaged.

I do hope that's more than wishful thinking ... I'm afraid that the Japanese nuclear industry has a long history of playing down incidents (though this is clearly more serious than anything they've had before) & the Japanese Govt has a clear interest in playing down the danger because there's practically nothing they can do about it - transport in the area is severely disrupted & they probably wouldn't be able to do a 50 km evacuation even if it was indicated.

[Ags]

The explosion wasn't "nuclear in nature." That is such a misleading statement. Even Chernobyl was not a nuclear explosion - it was a chemical explosion and a fire sending radiation into the air. The risk is the same as at Chernobyl - that a superheated core is exposed to the air, spewing out radiation.

It is impossible for a reactor to have a nuclear explosion, so the reassurances are misleading.

[brianb]

It is impossible for a reactor to have a nuclear explosion

Umm. As I understand the Chernobyl event, the core was unstable & went from 20% of its rated output to 500 times its rated output in less than 3 seconds - before the building was blown apart by expanding gas resulting from the rapidly increasing temperature.

I think that western power company reactors were designed in such a way that an event like that is exceedingly unlikely - unlike the Russian design which was a scaled-up version of the British design involved in the 1957 Windscale event - which was designed primarily to produce plutonium for weapons rather than electrical power. But highly enriched uranium can achieve criticality and indeed must do so (in a controlled manner) for a fission reactor to operate. There's no danger of a nuclear explosion so long as the control rods are fully inserted and that the fuel remains in its rods. If the cooling fails, the fuel can heat up enough to deform the rods & I'm afraid the safety designed in is forfeit.

[Ags]

Yes, Chernobyl's chemical explosion was powered by fission, but it was not remotely similar to a nuclear explosion. My point was nuclear reactors can do terrible things without turning into an atom bomb. An atomic explosion requires the explosive compression of specially shaped enriched elements.