Japan earthquake powerful enough to shift Earth’s axis

Many media are reporting today that the 8.9-magnitude earthquake in Japan on March 11, 2011 might have shifted Earth’s axis. Some experts say 8 centimeters. Others say 10 centimeters. EarthSky is checking with its scientists/sources and will record an interview on this subject in the coming week, as more details become known.

Earth’s axis of rotation is tilted at an angle of 23.5 degrees relative to the orbital plane at which Earth travels around the sun. This tilt causes our four seasons.

The tilt in Earth’s axis is strongly influenced by the way mass is distributed over the planet. Large amounts of land mass and ice sheets in the northern hemisphere make Earth top-heavy. Powerful forces such as those from thrust-earthquakes or asteroid impacts can change the distribution of land mass and alter Earth’s axis.

When Earth’s axis changes, the daily rotation of Earth can speed up or slow down much in the same way that a figure skater can change the speed of their spin by moving their arms up or down.

In a previous post, National Geographic News reports that:

• The 8.8 magnitude earthquake in Chile in February 2010 shifted Earth’s axis by 7.6 centimeters and shortened the length of the day by 1.26 millionths of a second.
• The 9.1 magnitude earthquake in Sumatra on December 2004 shifted Earth’s axis by 7.0 centimeters and shortened the length of the day by 6.8 millionths of a second.

While small changes in the tilt of Earth’s axis caused by the 8.9-magnitude earthquake in Japan in March 2011 – and other powerful earthquakes – will not have any noticeable effect on our day-to-day lives, these changes do serve to illustrate the power that can be unleashed by natural disasters.

Chile earthquake might have shortened Earth’s day, but how?