Alexandra Pope, staff writer
March 14, 2011 — Massive earthquakes like the one that struck Japan on March 11 do shift the earth's axis, but the difference is not noticeable in everyday life.
Astronomer Andrew Yee says even small earthquakes and powerful weather systems can cause minuscule changes in the earth's rotation. The bigger the earthquake, the bigger the change.
Yee compares the earth to a figure skater spinning around -- when a figure skater folds their arms into their body, they speed up; when they spread their arms out, they slow down. In the same way, “When we disturb the mass of the earth, it causes the earth to either speed up or slow down,” he explains.
Japan's meteorological agency says the epicentre of the earthquake was 500 kilometres long -- that's almost the distance between Hamilton, Ontario and Ottawa.
That's a lot of earth being moved at one time, so the impact on the earth's rotation was more significant, Yee says.
“It actually sped up the length of the day by 1.6 microseconds.”
A microsecond is one millionth of a second; that kind of change is imperceptible to all but the most sensitive instruments for measuring time.
“For everyday life it might not mean a whole lot,” Yee says, “but for somebody like NASA, (which is) interested in precise time when sending spacecraft to another planet ... this could have a longterm impact on navigating spacecraft.”
No evidence moon influences tectonic movement
What about the theory that massive earthquakes are more likely when the moon is closer to the earth?
That's not likely, Yee says.
“On March 19th we’re going to see a full moon, the closest moon of the year, which will cause an exceptional high tide because of the stronger gravitational interaction between the moon and the sun and the earth,” he explains. “But the fact is that the moon comes close to earth every month and we don’t see massive earthquakes.”
Yee adds that theories about astronomical causes of earthquakes are nearly impossible to test because scientists still aren't able to reliably predict when and where earthquakes will occur.