The earthquake that struck Friday off the coast of Japan was so strong it moved the island of Honshu 8 feet to the east and sped up the Earth's rotation by 1.6 microseconds, making the day just a little shorter, scientists said.

LOS ANGELES — The earthquake that struck Friday off the coast of Japan was so strong it moved the island of Honshu 8 feet to the east and sped up the Earth’s rotation by 1.6 microseconds, making the day just a little shorter, scientists said. A microsecond is one-millionth of a second.

A preliminary study by the Italian Institute of Geology and Volcanology indicate the quake may have shifted the Earth’s rotation axis by 3.937 inches, said Antonio Piersanti, researcher of the Rome-based institute, in an e-mailed statement Friday.

Earthquakes can involve shifting rock by several meters, changing the distribution of mass on the planet. This affects the Earth’s rotation, said Richard Gross, a geophysicist at the National Aeronautics and Space Administration.