The Great Seattle Quake Of 1995: What Had We Learned? Were We Ready?

THE PUGET SOUND AREA'S last sizable earthquake occurred nearly 30 years ago. What might happen in a major quake today? Scientists and government officials say this fictional scenario includes many distinct possibilities. --------------------------------

What all the Seattle survivors of the Great Quake of 1995 remembered was how long it went on.

A subduction-zone earthquake off Washington's coast had not been experienced for 300 years.

And although it registered a magnitude of 8.6 in the ocean - stronger than Alaska's disastrous 1964 earthquake - the epicenter's distance from the Puget Sound area meant the shaking seemed no worse here than the temblors of 1949 and 1965.

But the duration seemed endless. The Los Angeles earthquake of 1994 had lasted just 30 seconds. Washington's whopper lasted several sickening minutes.

"It seemed like several years," one woman said afterward.

The lengthy shaking destroyed dozens of structures that might have persisted through a shorter event.

Moreover, the earthquake could not have hit at a worse time. School was in session. Roadways were crowded. The temperature was below freezing when the power went out. Rain and sleet hampered rescue crews.

The 30-foot-high tsunami that slammed into Washington's coast after the quake was aggravated by winter winds and high tides, plowing into coastal communities, sloshing into marinas and pummeling the shoreline of Grays Harbor and Willapa Bay.

By the time the tsunami surged into Puget Sound the wave height was only 3 to 6 feet. But underwater landslides and crumbling cliffs created their own higher waves. Waterfront homes were awash, boats were hurled ashore, docks were turned to kindling.

It was at the water's edge that many of this earthquake's worst effects were experienced. All of Puget Sound's major ports were built on landfill and spongy river deltas. The quake's long duration provided enough time to liquefy the wet soil mixture. The foundations of the ports of Seattle and Tacoma began to slide into the deep waters of Elliott and Commencement bays.

The results were spectacular. Huge orange cargo cranes toppled. Container pads disappeared underwater. Docks nosed down like submarines. Back in 1994, Tacoma author John Nance, writer of a book called "On Shaky Ground," warned of this very thing.

"In one fell swoop," he forecast when interviewed, "an earthquake could literally destroy our ports . . ."

The soil under the Alaskan Way Viaduct turned to mush, its columns did the splits, and sections of the roadway pancaked down, crushing automobiles and halting rail traffic on the tracks underneath.

The Kingdome soil shifted enough to crack the stadium roof, though the intrinsic strength of the dome prevented a cave-in on the trade fair inside.

In adjacent Pioneer Square, the damage picture was more mixed. An estimated 40 percent of the buildings had been strengthened during remodeling and stayed intact. Unmodernized buildings of unreinforced brick simply gave way, however, crumbling into rubble.

The same liquefaction of loose fill and alluvial soils that plagued the ports extended up the region's river valleys. Newer warehouses and factories benefited from improved fastenings and a toughening of building codes that began in the early 1970s. But older buildings using tilt-up concrete walls broke.

The fate of other buildings was mixed.

Wood houses that were well-fastened to their foundations generally survived, though shelves toppled, chimneys cracked and power was lost. Brick homes lost some of their external facade, but their internal wood frames flexed and held.

A few steep hillsides slid, however, taking view homes with them. On Queen Anne Hill, homeowners who were giving thanks for having dodged that peril were hit with a flash flood when a metal water tower collapsed. Water towers proved to be one of the most vulnerable type of structures, leaving several of Seattle's hills without drinking water.

Downtown's new skyscrapers performed well. In a few spots windows, sheet metal and stone facings loosened and showered into streets below.

Older steel and masonry buildings had a mixed record. Their fate hinged on whether they had been seismically reinforced, as well as on their basic design and the soil.

Among those that fared poorly were buildings whose showy, expansive store windows facing the street left pressure on a few narrow columns. These "soft-story" ground floors collapsed toward the street, leaving the buildings looking as if they had kneeled down and leaned out over the sidewalk.

The Great Quake left bitter regrets.

In 1994, tax-weary Seattle voters had rejected a school bond issue designed in part to prepare older schools for earthquakes.

Many schools had already been improved or closed. But at others, left unchanged because of the failed bond, old chimneys slid, cornices crumbled and bricks came loose just as children were going to recess.

Bridge-strengthening programs seemed to pay dividends. The state had been doing seismic retrofits since 1972, strengthening more than half of the state bridges and overpasses in the Seattle area by 1994. The city had completed work on 11 of 25 identified problem bridges.

One of those improved just months before the quake carried foot passengers off the ferries into downtown. The bridge was jammed with people when the quake struck. It held.

Improvements on others were planned but did not come soon enough. The Fauntleroy bridge and the Magnolia bridge gave way, as did several small overpasses. Some of these bridges carried gas and water lines which sheered off, producing spectacular fountains of fire and spray.

Worst of all was a delay in fixing the Ship Canal Bridge on Interstate 5 just north of downtown Seattle. Planned improvements were just getting under way when the steel superstructure that jutted above the bridge piers broke, as consultants had feared it could.

The huge structure fell onto the concrete piers, and the upper road deck fragmented onto the lower. The state's major north-south artery was severed. Until traffic halted, autos dropped off the lip of the freeway like lemmings.

The convention center and Freeway Park, built over the freeway to more modern seismic requirements, weathered the quake just fine.

This scenario is fiction, of course.

The Great Quake hasn't happened in this area yet. Although a deep crustal quake with a magnitude of 6.0 to 7.5 is expected to occur somewhere in the Puget Sound basin about once every 35 years, the kind of subduction-zone quake described here might not happen for centuries.

But it could happen tomorrow.

Even less likely is a shallow quake of the Seattle Fault running under the city. The last time that occurred was 1,100 years ago.

But again, it could happen.

Are we prepared?

In 1975 the U.S. Geological Survey published a study estimating a 7.5 magnitude earthquake in the Puget Sound area would kill 2,200 and injure 8,700. Since then, geologists have learned of the potential for even more-serious quakes in this area, based on evidence of past upheavals.

Accurately predicting which structures would survive or fail is difficult, however, and the scenario above is at best an educated guess. Generally, newer is better than older. Wood and steel are better than unreinforced masonry.

Quakes are quirky, however. Their magnitude, duration, location and the soil they are shaking all can make a big difference in damage done.

The region is better prepared than in 1975. A majority of freeway bridges have been reinforced, noted Myint Lwin, the state bridges engineer in Olympia.

Building codes have steadily improved, with the last major change occurring in 1988. Beginning in 1995, rural Western Washington communities are expected to join urban Puget Sound cities in adhering to what are called Zone 3 earthquake standards in construction.

But no structure can be proofed against the worst imaginable earthquake. Early reports from Los Angeles suggested some bridges and houses designed to earthquake standards failed. And there is a limit to how much society can afford to spend on earthquake improvements, particularly when other dangers, from car accidents to murder, kill more people.

"If it costs $10 million to retrofit a building, would that money be better spent somewhere else?" asked Cliff Marks, an earthquake expert with Seattle's Planning Department.

Chances are, the kind of earthquake described here won't happen in our lifetimes. A quake will likely come, but it will probably be less disastrous.

The Earth makes no promises, however. And if a Seattle Fault quake occurred, it could easily be far worse than the scenario imagined here.