Last Friday’s quake in Japan has likely shortened the length of the planet’s day and shifted its axis, says a NASA scientist.
Using a United States Geological Survey evaluation of the fault responsible for the earthquake and how it slipped, Richard Gross has carried out some preliminary calculations of how the earthquake affected Earth’s rotation.
His calculations indicate that by changing the distribution of Earth’s mass, the Japanese earthquake has probably caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds.
His calculations also show that the Japan quake should have shifted the position of Earth’s figure axis, about which the planet’s mass is balanced, by about 6.5 inches, towards 133 degrees east longitude.
This will cause Earth to wobble a bit differently as it rotates, but won’t cause a shift of Earth’s axis in space, says Gross.
By comparison, last year’s magnitude 8.8 earthquake in Chile shortened the length of day by about 1.26 microseconds and shifted Earth’s figure axis by about three inches, Gross estimated.
Gross says that, in theory, anything that redistributes Earth’s mass will change its rotation.
“Earth’s rotation changes all the time as a result of not only earthquakes, but also the much larger effects of changes in atmospheric winds and oceanic currents,” he says. “Over the course of a year, the length of the day increases and decreases by about a millisecond, or about 550 times larger than the change caused by the Japanese earthquake.”
Gross adds that the position of Earth’s figure axis also changes by over three feet during the course of a year.
“These changes in Earth’s rotation are perfectly natural and happen all the time,” he says. “People shouldn’t worry about them.”