Change in the rotation of the earth

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The recent earthquake in Japan reportedly altered the Earth's angular velocity by a few microseconds, a change predicted through models rather than direct measurements. Precision in measuring the Earth's rotation is achieved using long baseline interferometry and ring laser interferometry, which can detect changes in the rotation axis with remarkable accuracy. Previous significant earthquakes, like those in Chile and Sumatra, did not show discernible effects in rotation changes, leading to skepticism among some researchers. The current models suggest even greater changes from the Japan quake, with expectations for confirmation from ongoing VLBI measurements. The discussion also touches on the reported displacement of the Earth's axis, with some sources citing a shift of 10 cm or more, prompting questions about the nature of this displacement.
starfish99
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Recent news articles say that the earthquake in Japan changed the angular velocity of the rotation of the Earth on its axis by a few microseconds. How do they measure the change in rotational speed to such accuracy?
 
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This is a predicted change based on measurements of the quake and on computer models of the solid Earth, not a directly measured change in the Earth's rotation axis or rotation rate.

We can measure the rotation axis and rotation rate of the solid Earth to an amazing degree of precision thanks to very long baseline interferometry. The uncertainties in these measurements are smaller (considerably smaller) than the polar motion and change in length of day predicted by the modelers. Experimentalists could not find any discernible effects from the 2010 Chilean earthquake or the Christmas 2004 Sumatran quake. Some experimentalists were nice to the modelers ("there are lots of confounding effects, yada, yada, yada") but others were not ("What change are you talking about?")

Since the modelers predict even greater changes for this Japan earthquake than they did for the Chilean or Sumatran quakes, I expect either confirmation of this by VLBI measurements (this will take another week or so) or I expect more experimentalists to join the not-so-nice camp.
 
starfish99 said:
Recent news articles say that the earthquake in Japan changed the angular velocity of the rotation of the Earth on its axis by a few microseconds. How do they measure the change in rotational speed to such accuracy?

Earth rotation rate can be monitored with ring laser interferometry. Ring laser interferometry utilizes the Sagnac effect.

Wikipedia article about the http://en.wikipedia.org/wiki/Sagnac_effect"

The page http://ringlaser.org.nz/content/about_us.php"
The accuracy of these particular ring laser interferometers is in the parts per billion range.
 
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How about the displacement of the axis by 10 cm (in some articles is even 10 inches)?
Does anyone here knows what do they mean by that? What kind of displacement?

Example of news piece:
http://en.ura-inform.com/neformat/2011/03/11/zemlja?nocache

It seems that everyone refers the information to the INGV, in Italy.
On their website I only found a brief note that says that the axis has moved by 10 cm:

http://portale.ingv.it/portale_ingv...11/terremoto-in-giappone/?searchterm=giappone
 

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