Change in the rotation of the earth

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Discussion Overview

The discussion centers around the impact of recent earthquakes, particularly the one in Japan, on the Earth's rotation and angular velocity. Participants explore the methods used to measure these changes, the accuracy of such measurements, and the implications of axis displacement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that changes in the Earth's rotation due to earthquakes are predicted based on models rather than direct measurements.
  • One participant mentions the use of very long baseline interferometry (VLBI) for precise measurements of the Earth's rotation axis and rate, highlighting the uncertainties involved.
  • Another participant introduces ring laser interferometry as a method to monitor Earth’s rotation, citing its accuracy in the parts per billion range.
  • A question is raised regarding the reported displacement of the Earth's axis by 10 cm or 10 inches, seeking clarification on what this displacement entails.
  • Participants express differing views on the reliability of predictions made by modelers compared to experimental observations from past earthquakes.

Areas of Agreement / Disagreement

There is no consensus among participants regarding the accuracy and reliability of the measurements and predictions related to the Earth's rotation changes. Multiple competing views remain on the interpretation of the data and the implications of the findings.

Contextual Notes

Participants note limitations in the measurements, including uncertainties and the potential for confounding effects that may influence the observed changes in rotation and axis 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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