NASA scientist: Chile earthquake may have shifted Earth's axis, shortened day

March 2, 2010

A scientist for NASA has said that the recent magnitude 8.8 earthquake in Chile, which killed at least seven hundred people, may have moved the Earth's axis, and caused the day to shorten.

Richard Gross, a scientist at the Jet Propulsion Laboratory in Pasadena, California, computed how the globe's rotation should have been altered by the earthquake; he and fellow scientists determined that the day had been shortened by approximately 1.26 microseconds (a microsecond is one millionth of a second).

Gross commented about his findings to the Bloomberg news agency in an email, saying: "[t]he length of the day should have gotten shorter by 1.26 microseconds. The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (equal to approximately eight centimeters or three inches)."

Gross compared the Chile earthquake with the 9.1 magnitude Sumatra earthquake in 2004 which generated a tsunami. According to him, that temblor shortened the day by 6.8 microseconds and moved the axis by about 2.3 milliarcseconds.

The scientist noted that the Chilean earthquake moved the Earth's axis more than the Sumatran one, despite not being as strong for two reasons. The first, he said, is because it was located in the mid-latitudes of the globe, which made it more effective in altering the axis. The other reason was that the Chilean earthquake fault was steeper than that in Sumatra, which results in more vertical motion and thus more change in the figure axis.

In an interview with Bloomberg Radio, David Kerridge, the head of Earth hazards and systems at the British Geological Survey in Edinburgh, Scotland, described how the earthquake may have caused such a change in the axis. "It’s what we call the ice-skater effect," Kerridge explained. He then described how when an ice skater executes a spin, if the skater pulls in his or her arms, the skater's rate of spin will increase. "It’s the same idea with the Earth going around. If you change the distribution of mass, the rotation rate changes."