Wednesday, February 24, 2021

The Nisqually earthquake 20 years later: We’ve made seismic improvements but there’s more work ahead

Our most visible response, the Alaskan Way Viaduct project, improved safety and helped transform Seattle's waterfront

By Mike Allende
After the Nisqually earthquake, the Alaskan Way Viaduct in Seattle was closed for inspections and repairs, and later strengthened to keep it safe for daily use. In 2019 the viaduct was replaced with the SR 99 tunnel.

It's been 20 years since the magnitude 6.8 Nisqually earthquake shook the Puget Sound region and we're still seeing its effects today.

On Feb. 28, 2001, hundreds of buildings were damaged and an estimated 400 people injured as the ground shook and rolled for 40 seconds. While bridges across the region by and large withstood the earthquake well, one of the most visible impacts was several columns supporting the Alaskan Way Viaduct in downtown Seattle cracked and sank, but did not collapse.

Seismic bridge retrofit, lifelines and greater resilience planning

Seismic retrofit work was already underway on our bridges and other infrastructure before 2001, but since then it's increased dramatically, including:
  • We've spent $144 million in bridge seismic retrofitting, completely retrofitting 323 bridges and partially retrofitting another 114, which still need some work. 
  • Working with state emergency managers and the Federal Emergency Management Agency (FEMA), we prioritized our seismic retrofit efforts along a "lifeline" designed to ensure emergency response and supplies can flow into the Puget Sound from the north, south and east. This lifeline identified and prioritized the most vital routes and bridges needed for transport during major emergencies. We are working on delivering a $171 million seismic retrofitting program that should complete lifeline retrofitting over the next 10 years.
  • New projects have replaced aging bridges with updated structures built to modern-day standards. Examples include:
    • The new SR 520 bridge, which opened in 2016
    • In Pierce County, 18 new seismically-updated bridges or overpass structures have been built as part of the I-5/SR 16 Tacoma/Pierce County HOV Program and the I-5 Lakewood to Joint Base Lewis McChord projects.
    • Two new bridges over the Puyallup River (SR 162 & SR 167)
The new and more seismically-resilient Mukilteo Multimodal Ferry Terminal opened in December and work continues on Colman Dock in downtown Seattle to build a new, seismically improved multimodal terminal. Going forward, terminal repairs/upgrades are included in Washington State Ferries' long-range plans (pdf 11.7 mb).

From Alaskan Way Viaduct to SR 99 tunnel

In perhaps the most visible response, that powerful earthquake also jolted our agency to accelerate existing conversations about how to replace the aging Alaskan Way Viaduct, the double-deck concrete highway that carried 100,000 vehicles a day along Seattle's waterfront via SR 99. A parallel conversation also began about the deteriorating 70-year-old seawall that protected the waterfront's loose fill soils from Elliott Bay.

Twenty years later, those conversations have utterly transformed central Seattle's waterfront. Traffic on SR 99 now travels beneath the ground in the 2-mile SR 99 tunnel,  built to withstand strong earthquakes.

The last visible trace of the looming concrete fence that once separated Seattle from Elliott Bay was removed in November 2019. Seattle's new seawall opened in 2017, built to modern seismic and environmental standards and atop that seawall, the city of Seattle is building a new waterfront street flanked by new public space and multimodal transportation facilities.

Today, the Alaskan Way Viaduct Replacement Program is almost complete. The Battery Street Tunnel that once linked to the viaduct's northern end is gone, and the chasm it cut through neighborhoods near the Space Needle is replaced by a surface street. The final project of the program is set to begin construction later this year, which includes a new pedestrian plaza connecting Seattle's sports stadiums to the waterfront.

Looking back but planning for the future

Timelines have been hard to gauge during the COVID-19 pandemic, when weeks blend and a month can feel like a year. But the 20th anniversary of the Nisqually earthquake is a good time to pause and take stock of all that has been accomplished.

We still have more work to do, but in the 20 years since the ground shook from Olympia to British Columbia, we've made major safety improvements across the state to help us all have safer, more resilient infrastructure across the state.