In 2011, a magnitude 9.0 earthquake shifted the planet’s axis and shortened Earth’s days

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In March 2011, a 9.0-magnitude earthquake struck off the eastern coast of Japan, shifting the Earth’s axis, and shortening the days on Earth.

The earthquake—the most powerful ever to strike the country—shifted the planet’s axis by about 17 cm (6.5 in), and may have moved the main island by about 2.4 meters (8 ft). Like other similar large earthquakes, it also changed the rotational speed of the Earth.

“Earthquakes can change the Earth’s rotation by rearranging the Earth’s mass. This is what a snowboarder does to make herself spin faster. She moves her arms closer to her body, and she moves her mass closer to the axis around which she rotates,” explained Dr. Richard Gross of the Propulsion Laboratory. NASA’s Jet told Popular Mechanics in 2011: “And earthquakes do the same.”

“This earthquake must have moved the mass on average a little closer to the Earth’s axis of rotation to make the Earth spin faster and the length of the day a little smaller.”

By looking at models of Earth’s mass distribution before the earthquake and using estimates of how the fault slides during an earthquake, Gross was able to work out how the mass distribution changed.

“Then, by conserving angular momentum, if I know how to rearrange the Earth’s mass, then I know how the Earth’s rotation has changed,” he added.

In all, the earthquake accelerated the Earth’s rotation by about 1.8 microseconds (1.8 millionths of a second). By comparison, the Indonesian earthquake in 2004 speeded up Earth’s day by an estimated 2.68 microseconds.

Earthquakes are not the only events and factors that affect the speed of Earth’s rotation.

After the 2004 Indonesian earthquake, Dr. Benjamin Fung Chau, of NASA’s Goddard Space Flight Center, explained that “any terrestrial event that involves mass movement affects the Earth’s rotation, from seasonal weather to driving a car.”

There are all sorts of factors that affect the speed of rotation, such as changing sea levels and shifts within the Earth, although the biggest factor is that the Moon is moving away from Earth (who can blame it) and when the two bodies interact, the result is Earth slowing down, albeit That with bursts of speed now and then.

By looking at ancient coral reefs, scientists have discovered that the Earth was spinning much faster 444-419 million years ago. Every day, the coral puts on a delicate layer of calcium as it grows. Since corals grow more in the dry season than in the wet seasons, you can then count the lines of calcium carbonate sediments in each season and calculate how many days there have been in a year. Using this method, the team determined that the Earth had 420 days a year 444-419 million years ago, before the Moon’s influence slowed down.

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