Sunday, March 20, 2011

Japan Earthquake ~ Earth shifts on axis... what does that mean?

Prof. Ehud Behar, Head of ASRI Space Research, Technion - Israel Institute of Technology, explains the science behind the earth's shift on its axis that resulted from the catastrophic earthquake in Japan in March 2011.

Q: Since the earthquake in Japan, we are told the earth shifted on its axis? What does that mean?

A: When the ground moves and reassembles itself closer to Earth's rotation axis, Earth spins a little bit faster.
This is just like an ice skater pulling its arms in to accelerate its spin and is based on what in physics we call the conservation of angular momentum: a reduced radius of motion causes a faster angular speed.

As opposed to the skater, the effect here is minuscule as the amount of ground shifting compared to Earth's total mass is very small. The change in the duration of the day amounts to a few millionths of a second out of 24 hours - didn't you feel you have less time for everything?
As far as I can tell, the rotation axis-shift is a misconception. The same law of physics - conservation of angular momentum - does not allow the change of the rotation axis without external intervention, such as an impact of a meteor, or a passing by of a heavy planet. What happens with internal motions, as in an earthquake, is that the distribution of matter on Earth changes, so its axis of symmetry (around which mass is symmetrically distributed) might change, but not it rotational axis. 

1 comment:

  1. English tip:

    We would not refer to a figure skater as "it".

    We would say, "This is just like an ice skater pulling their arms in to accelerate their spin..."