Week of Feb. 27, 2006

Five years later impacts of Nisqually Earthquake linger

The Nisqually Earthquake that struck five years ago this week looms large in the memories of those who lived through it. And, some of the damage is still being addressed by the King County Department of Transportation.

The earthquake hit on the morning of Feb. 28, 2001, and lasted 40 seconds. It had a magnitude of 6.8 on the Richter scale, and was felt as far away as Salt Lake City.

The earthquake damage to King County roads, bridges, transit facilities, and buildings and runways at King County International Airport (Boeing Field) totaled about $7 million. Most of the transportation-related repairs were completed within a few weeks, but two projects still need to be tackled.

Despite immediate post-quake repairs, the county needs to replace the South Park Bridge and complete rehabilitation of the main runway at Boeing Field.

Only three county bridges were damaged during the earthquake, with the South Park Bridge over the Duwamish River being the most heavily damaged. It cost nearly $700,000 to repair the aging structure, but operational capability was restored in just 25 days. The bridge suffered damage to the alignment of the draw spans, cracking of concrete piers and rails, and widespread settlement of the south end approach from liquefaction of the underlying soils. The county’s bridge engineers and consultants designed repairs that were constructed by contract and county crews. See a photo gallery of damage to the South Park Bridge and how it was repaired.

The county considered five alternatives to fix the bridge, including rehabilitating the existing structure, constructing a fixed-span or movable-span bridge and removing the bridge entirely. Recently, the decision was announced that a movable-span bascule bridge is the best replacement option. This alternative also presents the fewest community impacts.

The cost of constructing a new bascule drawbridge is estimated at $90 million. If funding cannot be secured, the rapidly deteriorating bridge will need to be dismantled and removed by the end of the decade due to safety concerns. In addition to severing the community’s main transportation route, removal of the bridge will force more than 20,000 vehicles a day on to nearby commuter and freight routes such as the 1st Avenue South Bridge, the West Seattle Bridge, State Route 99 and Interstate 5.

At the airport, the paved surfaces of KCIA’s primary runway and Taxiway Bravo are near the end of their useful lives, and also were damaged during the 2001 Nisqually Earthquake. While most of the earthquake damage was repaired immediately, the pavement continues to settle and deteriorate. If not addressed, these problems will require increasingly frequent repairs and could lead to increased runway and operational restrictions. A major runway rehabilitation project will begin later this summer.

Excluding the bridge and runway repairs, damage to King County roads from the Nisqually Earthquake was relatively minor. On a strict damage comparison, there were more road maintenance projects to complete and costs were significantly higher after the major winter storms in 1995, 1996 and 1997.

Still, the after-effects of the earthquake kept the department very busy. Immediately following the quake, Road Maintenance crews began emergency protective measures to increase public safety. Initially roadways and bridges on critical lifeline routes were checked for structural problems. This was followed by road patrols to examine all of the transportation infrastructure in the unincorporated areas.

Complaints were investigated and traffic barriers were put up as needed to close roads and re-route traffic. The maintenance crews identified a total of 14 site-specific earthquake repairs. Most of these involved road/shoulder failures were the pavement surface dropped several inches, or slides that covered roads with mud and debris. Most of that repair work was completed within six weeks.

King County’s aggressive bridge seismic retrofit program saved many structures from being damaged. It was started in 1994, and by the end of 2005 the Roads Division completed 110 of the 115 seismic bridge projects.

For Metro Transit, most of the 105 quake-related damage reports were minor. The biggest inconvenience was that buses had to be rerouted off the Alaskan Way Viaduct for three months.

Two significant post-quake transit projects were the bracing of walls at Metro's Power Distribution Headquarters, and repair of trolley overhead wires in the Pioneer Square area. The overhead wires had been attached to an adjacent building at Second and Main, but falling bricks knocked them to the ground. Because trolley wires require several thousand pounds of tension to keep them tight and level, they could not be reattached to the damaged building out of concern they would pull off more pieces. Instead, Metro Transit crews erected a 65-foot wooden pole to secure the wires. The pole had to be planted near the railroad tracks 30-feet below street level, and reach up 25-feet above the street. See a photo gallery of the installation.

In 2002, on the one-year anniversary of the earthquake, King County Executive Ron Sims reflected on how county workers had responded immediately to protect the public and begin repairs.

“We know the Nisqually Earthquake was a wake-up call, but we had more going for us than just luck,” said Sims. “We had an army of dedicated employees who were ready and willing to do whatever needed to be done.”

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