Earthquake Damage Is Assessed in Northwest

A pair of mild aftershocks rolled through western Washington on Thursday as officials assessed the damage from the magnitude 6.8 quake that rocked Seattle a day earlier--and felt lucky that things weren’t worse.

Seismologists cited the fact that preliminary measurements showed the temblor produced barely one-tenth the horizontal surface shaking of the 1994 Northridge quake.

The findings provided an important clue as to how Seattle came away from the quake with just a single heart attack death and total losses now estimated at $3.6 billion. The Northridge quake, while similar in magnitude, resulted in 57 deaths and damage of $40 billion.

“They are getting some real damage up there, but it’s not at all comparable to Northridge,” said Thomas Heaton, professor of earthquake engineering at Caltech.

With the perennial Seattle drizzle beginning to fall, attention turned Thursday to the possibility of landslides--which already have destroyed several homes, buried roadways and temporarily diverted the Cedar River where it flows through suburban communities east of here.

The Pacific Northwest’s unusually dry winter has left the soil less vulnerable to sliding than it otherwise would have been. “But right now, you can see the rain we’re getting. That could cause an increase in landslides in the next day or so,” said Jerick Bergsma, research assistant at the University of Washington seismology laboratory.

After previous deep quakes in the Seattle-Tacoma region, said David Clark of the American Institute of Architects’ disaster preparedness team, landslides have occurred about three days later.

Clark said there is mounting evidence of landslide damage. “We are now discovering quite a bit more damage to the earth and roads and bridges than was at first obvious,” he said.

After touring a region of broken roads, damaged bridges and crumbling older buildings--which largely escaped major structural failures and high casualties--Gov. Gary Locke said Thursday: “While this was a very strong earthquake and the damage will be extensive, thank goodness there was no loss of life. I think that was because people kept their cool, by and large, and knew what to do.”

The total number of reported injuries climbed Thursday to 320, with at least four people remaining in serious condition.

Federal Emergency Management Agency Director Joe Allbaugh said he would ask President Bush to declare a state of emergency as soon as possible to make federal disaster relief available. Bush did so late Thursday night.

“The report I’m going to give him is that Washington was prepared and they’ve done a good job in handling this,” Allbaugh said. “Everybody ought to be thankful and proud of the job that everyone’s done over the last 24 hours.”

Preliminary FEMA estimates set damage at $2 billion, and total economic losses--including property damage and interruption of business--at $3.6 billion.

Aftershocks Were a Surprise

The two mild aftershocks Thursday surprised seismologists, who had predicted little likelihood of significant tremors because of the 36-mile depth of the quake. A 3.4-magnitude tremor struck at 1:10 a.m., followed by a mild 2.7 quake at 6:23 a.m.

Both were centered 14 miles northeast of Olympia, Wash., in roughly the same location as the original quake.

“We did say we weren’t expecting aftershocks, and here we’ve had two of them, which shows you we’re learning from each of these experiences as we go,” said Bergsma.

“We need to keep our attention up,” Allbaugh cautioned. “Everyone should be sensitive over the next couple of days to additional aftershocks. We need to not treat this as an incident that has gone by the wayside.”

After Interstate 5 and Seattle arterials remained a congested mess for much of the day, the state Department of Transportation reopened the elevated waterfront viaduct that is one of downtown Seattle’s main throughways.

But a major bridge linking downtown to the city’s Magnolia district remained closed, with needed repairs estimated at $1 million or more.

The city’s main downtown freeway onramp also was shut down, along with sections of five state highways and a bridge in Bremerton.

Seattle-Tacoma International Airport was operating at only half capacity because air traffic controllers still were using a temporary tower put together after the quake damaged windows and supports.

The state Capitol complex in Olympia remained closed, idling 10,000 workers. And Pierce County sheriff’s detectives continued the search for a child rape suspect who had escaped from a Tacoma courthouse when the earthquake interrupted his arraignment.

Two Dozen Structures Ruled Uninhabitable

At least two dozen buildings in Seattle were deemed uninhabitable or recommended for such a designation--with 29 others yellow-flagged for limited entry.

“The biggest news is there is no news,” Seattle Mayor Paul Schell said. “The damage we’ve suffered is nothing close to what could have been. . . . At this point, our job is to get the city back to normal. We need to get a clear assessment of all the damage, determine the costs and funding possibilities and to get repairs underway.”

City officials said that the $30 million Seattle has spent over the last year retrofitting bridges and overpasses for seismic safety was a big factor in keeping access to most of the city open.

The fact that older Seattle dwellings tend to be made of pliable wood rather than brittle masonry also helped, said Charles Roeder, civil engineering professor at the University of Washington.

In general, the city’s earthquake codes for new buildings are comparable to those in Los Angeles or San Francisco, although Seattle does anticipate slightly milder earthquakes, Roeder said.

“I think you would find the performance of our newer buildings wouldn’t be substantially less than what you see in Los Angeles,” he said.

The question in many minds since the quake is why Seattle fared so much better than Southern California with a 6.8 quake--nearly equal to the Northridge temblor.

The answer, in new horizontal velocity measurements released Thursday, is that the 36-mile-deep quake, much farther below the surface than the Northridge quake, provided far slower horizontal surface movements.

“It produced shaking of much less violence than we would get from a shallow, crustal earthquake,” said Bill Steele, the University of Washington seismology lab coordinator.

According to figures from the National Earthquake Information Center in Golden, Colo., the worst shaking Seattle felt was about 16 centimeters--a bit more than 6 inches--per second, only about 15% of the 105 centimeters--about 41 inches--of movement seen near the epicenter of the Northridge quake.

Several central Seattle locations showed movement of only 5 to 8 centimeters--roughly 2 to 3 inches--per second. The general threshold for significant structural damage is about 30 centimeters--nearly 12 inches--per second, and 105 “is more than a meter per second,” Heaton said. “This is violent; you wouldn’t be able to stand upright. Literally, it would throw you to the ground.”

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Ground Movement

Northridge*: 105

Everett: 4

Bremerton: 14

Seattle Airport: 16

Shelton: 15

* Median readings within 10-mile radius

Data prepared by the U.S. Geological Survey show the shaking intensity in the Seattle area Wednesday was only about 10% of the levels seen in the epicentral area of the Northridge quake. The readings show peak ground velocity in terms of centimeters per second. In Northridge, within six miles of the rupture zone, it was a median of 105 centimeters, or a little more than a meter per second.

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Source: U.S. Geological Survey

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Researched by KEN REICH / Los Angeles Times

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