Seismic Planning

What & Why

Over the past several decades, Seattle Public Utilities (SPU) has invested hundreds of millions of dollars in water system infrastructure improvements. These improvements include:

  • Federal- and state-mandated water projects
  • Rehabilitation and replacement of aging infrastructure
  • Seismic upgrades to selected facilities

All new projects meet or exceed current seismic standards. To date, SPU has invested more than $100 million in seismic upgrades to existing water infrastructure. Completed and future seismic upgrades will provide more protection of the water system during an earthquake and decrease system disruptions after an earthquake.

The 2018 Seismic Study:

Seattle’s path to building one of the most earthquake-resilient drinking water systems in the nation

Updated December 7, 2018

Nearly 30 years ago, SPU began retrofitting Seattle’s regional drinking water system to withstand the kind of earthquake that occurred in Alaska on November 30, 2018. This includes more than $100 million in seismic upgrades completed to date.

When an earthquake similar to the one in Alaska hit Seattle in 2001 (the Nisqually earthquake), the water system, that serves 1.4 million people in our area, was resilient and experienced only minor damage.

In recent years, new information has emerged about the Seattle Fault Zone and Cascadia Subduction Zone earthquakes that was not recognized 10 to 20 years ago. This led SPU to embark on a comprehensive, three-year seismic analysis of Seattle’s drinking water system.

The recently completed 2018 seismic study supplements an earlier SPU seismic study conducted in 1990 and analyzes the performance of the drinking water system using new information about earthquakes.

The 2018 study provides our region with a good understanding of how the drinking water system will withstand a major, catastrophic earthquake, which has a 15 to 20 percent chance of occurring in Seattle in the next 50 years.

Based on the study’s findings, SPU is developing short- and long-term plans, covering the next 50 years, that put the utility on a steady path for making significant infrastructure investments and building one of the most earthquake-resilient drinking water systems in the nation.

Information about how Seattle residents and businesses can prepare for an earthquake and other emergencies can be found on Seattle’s Office of Emergency website .

Links to the 2018 seismic study are available below, including the 16-page Executive Summary, which contains all the conclusions and essential content of the full study.

Note: Sections 3 and 4 of the study contain information that is protected by the Department of Homeland Security and not available for public safety reasons.

Regional water system resiliency

SPU has also been a regional leader in helping to develop water system resiliency. SPU is a charter member of The Water Supply Forum, which recently completed a regional earthquake vulnerability assessment. This assessment will help water utilities in King, Pierce and Snohomish counties:

  • Evaluate and increase our region's existing water supply systems resiliency
  • Plan for potential water supply disruptions

Additionally, SPU is working with other water utilities around the country through the Water Research Foundation and the American Society of Civil Engineers to share water system seismic resiliency improvement methodologies and approaches, and to develop seismic standards for new water mains.