Quake so powerful, it shifted Earth's axis

LOS ANGELES - Friday's magnitude 8.9 earthquake in Japan shifted Earth on its axis and shortened the length of a day by a hair. In the future, scientists said, it will provide an unusually precise view of how Earth is deformed during massive earthquakes at sites where one plate is sliding under another, including the U.S. Pacific Northwest.

The unusually rich detail comes from an extensive network of sensors that were placed at sites across Japan after that country's Kobe earthquake of 1995, a magnitude 6.8 quake that killed more than 6,000 people because its epicenter was near a major city.

"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, at a Saturday news conference at Caltech in Pasadena. "This is overwhelmingly the best-recorded great earthquake ever."

Already, slightly more than 36 hours after the quake, data-crunchers had determined that the temblor's force moved parts of eastern Japan as much as 12 feet closer to North America, scientists said - and that Japan has shifted downward about two feet.

Jones said that the USGS had determined that the entire earthquake sequence - including associated foreshocks and aftershocks - had so far included 200 temblors of magnitude 5 or larger, 20 of which occurred before the big quake hit. She said the aftershocks were continuing at a rapid pace and decreasing in frequency although not in magnitude, all of which is to be expected.

Researchers have a laundry list of items they hope to gather data on.

California Institute of Technology geophysicist Mark Simons said that knowing how much the land had shifted during the quake and its aftershocks would help scientists understand future hazards in the region and allow them to plan accordingly.

A colleague of his, Caltech seismological engineer Tom Heaton, said the tragedy would provide unprecedented information about how buildings hold up under long periods of shaking - and thus how to build them better.

"We had very little information about that before now," he said. Though precise numbers are not yet available, he predicted that the data would show that buildings in Japan were subject to a full three minutes of shaking.

Many of the lessons, however, will apply to other parts of the world than California, because the state's fault topography is different from the one involved in the Japanese quake. The earthquake that struck the New Zealand city of Christchurch on Feb. 22 is probably more analogous to what is likely to occur in California, because it occurred along a fault running very close to an urban area.

Geological evidence and historical records of tsunami deaths in Japan - from giant waves believed, based on modern analysis, to have come from a Cascadia quake - suggest that the most recent large earthquake in the Pacific Northwest occurred in 1700. It was probably larger than Friday's earthquake in Japan.

Another massive quake in the Pacific Northwest is "inevitable," the USGS's Jones said, though it may not occur for hundreds of years.