Earthquake moved Puget Sound

THE ASSOCIATED PRESS

SEATTLE -- The earth moved during the magnitude 6.8 Nisqually Earthquake, scientists say.

And they don't just mean it shook. Ground around Puget Sound moved more during the Feb. 28 earthquake than it normally does all year.

"Not only that, but it moved in the complete opposite direction of what we've observed from year to year," said Anthony Qamar, state seismologist and a research associate professor in earth and space sciences at the University of Washington.

Qamar works on a project called PANGA -- Pacific Northwest Geodetic Array -- which uses global positioning information to measure movement of the ground each year in Washington and Oregon, relating it to a fixed point farther east.

Typically, PANGA has found, the central Puget Sound region moves 3 to 5 millimeters east-northeast each year.

But after the quake, GPS sensors found that a Coast Guard station at Point Robinson, on the eastern edge of Maury Island, had moved 8 millimeters to the south-southwest. The UW campus, meanwhile, moved 5 millimeters south-southwest. Satsop, between the quake's epicenter and the coast, moved about 6 millimeters west and Pacific Beach, on the coast, moved northwest about 4 millimeters.

The quake's focus, or hypocenter, was about 34 miles below the Nisqually River delta, north of Olympia. Actual movement there was probably about a meter -- more than 3 feet, Qamar said, but the depth of the quake meant dislocation at the surface was far less.

While there are no measurements yet to back him, Qamar expects data will eventually show that areas west of the epicenter -- at the Nisqually River delta north of Olympia -- rose as much as a half inch, and that areas to the east dropped about one-third inch.

At Neah Bay, the northwesternmost point of Washington state, annual movement is double that of the central Sound -- about 10 millimeters, or around a half-inch. That's because the coast is closer to the zone where the Juan de Fuca plate is slowly diving below the North American plate.

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