Seismic Planning

Photo of Myrtle Tank construction
Seismically upgrading Myrtle Tank No. 2 with base isolators

 

Photo of pipe installation in Pioneer Square
Earthquake resistant pipe installation in Pioneer Square

The Puget Sound Region is one of the most seismically active regions in the United States. Moderate to large earthquakes that originate 20 to 40 miles underground struck Seattle in 1949, 1965 and 2001. The Seattle Fault Zone which has produced devastating shallow earthquakes similar to the 1995 Kobe and 2011 Christchurch earthquakes runs from the Kitsap Peninsula through Seattle to the Cascade foothills. Additionally, great subduction zone earthquakes similar to the 2011 Tohoku, Japan earthquake may occur off the Washington coast.

Graphic of the regional earthquakes described above

In 1990, Seattle Public Utilities (SPU) completed a water system seismic study and began an upgrade program that led to approximately $100 million in upgrades. This study was updated in 2018 to reflect hazards from a Seattle Fault earthquake and incorporates the latest seismic code updates. SPU is currently evaluating its drainage and wastewater system as well.

Making the SPU water system seismically resilient will take decades. SPU is improving its emergency preparedness and response capabilities to mitigate seismic effects in case a catastrophic earthquake occurs before the system can be made seismically resilient. Seattle residents are encouraged to develop their own emergency preparedness plans and resources. Information about how Seattle residents and businesses can prepare for an earthquake and other emergencies can be found at the Seattle Office of Emergency Management.

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 (pdf). 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.