Earth Shifts on Its Axis, Day Shortened After Japan Quake

Friday's magnitude-8.9 earthquake in Japan was so powerful it shifted Earth on its axis and slightly shortened the length of a day, and will help scientists plan for the future, earthquake experts at Caltech said Saturday.

The quake—said to be the fifth most powerful since 1900—and ensuing tsunami, killed more than 1,000 people in the island nation, and thousands more are missing. It also caused serious problems at three nuclear plants in Japan, prompting the evacuation of 200,000 people.

The resulting tsunami also affected the Southland, with wave surges capsizing boats on Catalina Island and causing a surge in King Harbor in Redondo Beach that  was believed responsible for a boat breaking free and slicing a dock in two.

But the quake provided valuable data for earthquake scientists, because an extensive network of sensors were placed throughout Japan after that country's magnitude-6.8 Kobe earthquake in 1995 that killed more than 6,000 people because its epicenter was near a major city.

At a news conference Saturday, scientists at Caltech said it will provide a more precise view of how Earth is deformed during massive earthquakes at sites where one plate is sliding under another, including the Pacific Northwest in the United States, the Los Angeles Times reported.

“The Japanese have the best seismic information in the world,” said Lucy Jones, chief scientist for the Multi-Hazards project at the U.S. Geological Survey. “This is overwhelmingly the best-recorded great earthquake ever.”

Analysts have determined that the earthquake's force moved parts of eastern Japan as much as 12 feet closer to North America, and Japan has shifted downward about two feet.

The temblor also should have caused Earth to rotate somewhat faster, shortening the length of the day by about 1.8 microseconds.

Jones said the U.S. Geological Survey determined that the entire earthquake sequence—including foreshocks and aftershocks—had so far resulted in 200 temblors of magnitude 5 or larger, 20 of which occurred before the big quake hit.

She said the aftershocks were continuing but decreasing in frequency, although not in magnitude, which was to be expected.

Caltech geophysicist Mark Simons said that kind of information will enable scientists to understand future hazards in the region.

Caltech seismological engineer Tom Heaton said the devastating temblor will provide more information about what happens to buildings when they shake for long periods, and how to construct them so they will survive massive quakes.

“We had very little information about that before now,” he said.

Though the data is still being processed, he said it will probably show that the shaking lasted for three minutes.

Another massive earthquake in the Pacific Northwest is “inevitable,” although it may not strike for hundreds of years, Jones said.

“They have an opportunity,” she said. “This will help the Pacific Northwest understand what they should be ready for. I wouldn't be sleepless in Seattle, but I'd be studious.”