Change in the rotation of the earth

[starfish99]

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?

 

[D H]

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.

 

[Cleonis]

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.

 

[nasu]

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

 

[PJC01]

I can confirm that the earthquake in Japan did indeed cause a change in the angular velocity of the Earth's rotation. This phenomenon is known as the "earthquake effect" and has been observed in past seismic events.

The change in rotational speed of the Earth is measured using highly sensitive instruments called seismometers. These devices are specifically designed to detect and record the movements of the Earth's surface, including changes in rotational speed.

To measure the change in rotational speed, scientists use a technique called interferometry. This involves comparing the signals recorded by multiple seismometers at different locations and using mathematical calculations to determine the exact change in rotational speed. This method allows for a high level of accuracy, with changes as small as a few microseconds being detectable.

It is important to note that while the change in rotational speed may seem small, it is still significant in terms of the Earth's overall rotation. This change can have an impact on various natural processes, such as the length of a day and the Earth's magnetic field.

In conclusion, the change in the rotation of the Earth caused by the earthquake in Japan is a well-documented and scientifically measured phenomenon. Through the use of advanced technology and mathematical techniques, scientists are able to accurately measure and track these changes, providing valuable insights into the Earth's dynamic nature.