Tony Overman/The Olympian
Cross traffic, house-lined hillsides and its mountain namesake are rare sites for the crew of the Rainier, a research vessel with the National Oceanographic and Atmospheric Administration, shown as it sits in Puget Sound near Tacoma on Tuesday afternoon. The ship usually operates in the oceans and bays of Alaska.

Jim Gardner, a U.S. Geological Survey marine geologist, is using information from the Rainier's high-resolution sonar to develop three-dimensional maps.

Survey team seeks signs of damage

Earthquake might have triggered slides under Puget Sound

JOHN DODGE, THE OLYMPIAN

"The value of this project is getting a snapshot of what the deltas look like before the next earthquake."--Jim Gardner, Marine geologist

COMMENCEMENT BAY -- The most detailed profile ever of three major river delta bottoms in Puget Sound is under way this week in response to the Feb. 28 Nisqually Earthquake.

The National Oceanic and Atmospheric Administration ship Rainier, a high-precision survey vessel, is searching for underwater landslides and other potential hazards in the Nisqually Reach, Tacoma's Commencement Bay and Seattle's Elliot Bay.

Equipped with some of the most advanced sonar equipment available, the Rainier and six launches are meticulously mapping the floor of Puget Sound.

The work focused on Commencement Bay on Tuesday and turns today to the Nisqually Reach -- near the 6.8 magnitude quake's epicenter.

"We're looking for large failures," said Jim Gardner, a U.S. Geological Survey marine geologist assigned the task of plotting and analyzing the data. "We haven't seen anything worth noting yet."

However, Gardner said river deltas are notoriously unstable. They are home to huge deposits of river sediments that are prone to landslides even without an earthquake.

Gardner said the detailed analysis of the data won't be completed for two weeks. It will be conducted by a team of geologists in Menlo Park, Calif.

Mapping the floor

Even if the survey work doesn't uncover anything geologically unusual or any damage to port structures, it will provide valuable data for updating navigation charts, ship Cmdr. Dan Herlihy said.

Navigation data for some areas of Puget Sound are decades old and were completed with outdated equipment, Herlihy said.

Echo sounders, sonar, computers and other equipment aboard the Rainier and its launches are capable of gathering data used to create high resolution, three-dimensional models of the river delta floors.

On Tuesday, launches fanned out from the Rainier, which was anchored in Vashon Island's Quartermaster Harbor. The small boats traveled along set routes within the bay, taking 700 to 800 soundings a second.

At night, the data collected is downloaded and processed on computers on the Rainier.

"The launches are the work horses," Ensign Kristie Twining said as her launch worked along the shoreline near the Browns Point Lighthouse.

Twining is a member of the NOAA Corps, America's seventh -- and smallest -- uniformed service. About half of the 50-member crew are Corps members and the rest are civilians.

Taking a snapshot

The Rainier is based in Seattle, but spends about seven months of the year in Alaska, conducting hydrographic surveys used to update navigation charts.

"We would have been heading for Alaska by now, if it wasn't for this assignment," ship officer Daniel Karlson said.

The Rainier is the only vessel of its kind on the West Coast, Herlihy said.

Commissioned in 1968, the 231-foot-long vessel is named after Mount Rainier.

On Tuesday, the ship's namesake loomed on the horizon, framed by a clear blue sky.

The calm, windless day belied the 45 seconds of geological havoc experienced in South Sound three weeks ago.

Gardner said the fact the earthquake did not generate a tsunami indicates the Puget Sound floor was not the scene of a major failure that would have displaced water, forming a tidal wave.

Because the current picture of the Puget Sound bottom is so blurry, there's no way of knowing if any landslide detected in this survey is a result of the recent earthquake or past events, Gardner said.

"The value of this project is getting a snapshot of what the deltas look like before the next earthquake," Gardner said.

John Dodge covers the environment and energy for The Olympian. He can be reached at 754-5444.

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