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INGV's report, which came hours after the devastating incident, is equivalent to "very, very tiny" changes that won't be seen for centuries, though, Canadian geologists say.
Only after centuries would a second be lost as each day is shortened by a millionth of a second, according to University of Toronto geology professor Andrew Miall.
"Ten inches sounds like quite a lot when you hold a ruler in front of you. But if you think of it in terms of the earth as a whole, it's absolutely tiny; it's minute," he said.
"It's going to make minute changes to the length of a day. It could make very, very tiny changes to the tilt of the earth, which affects the seasons, but these effects are so small, it'd take very precise satellite navigation to pick it up."
The earth's rotation will now shift at a different speed because the globe's mass has been redistributed, said Michael Bostock, a University of B.C. earthquake seismology professor.
He used an analogy of a figure skater pulling in his or her arms to spin faster because weight has been reorganized.
"Ultimately, if you change the length of day, you can change the length of time a given point on earth receives sunlight and doesn't receive sunlight," he said. "But will this affect us in our lifetimes? Absolutely not."
The researchers said that while the minuscule change may be completely undetectable, it still illustrates the punch behind the Japan's massive earthquake.
Last year, NASA reported that a 8.8-magnitude earthquake that hit Chile shorted the day by 1.26 millionths of a second, according to computer-model calculations.
NASA had estimated that the Chilean earthquake shifted the globe's axis by about 10 centimetres, National Geographic reported at the time.
INGV, which is Europe's largest research institute to monitor geophysics, said the impact of Friday's event was "much greater" than 2004's notorious Sumatra earthquake, which clocked in at a magnitude of 9.1.
Well if they can be sure of such claims inside of 24 hours since the quake, then they sure as hell know precisely what is out there and are able to measure precisely what effect it's having on the planet's speed of rotation and length of orbit.
Immediately after last year's 8.8 in Chile someone made the same claim about the Earth's axis shifting... it contested as being rubbish a few days later.