By Emily Keller-O'Donnell
July 11, 2023
The passage of a Washington State bill providing planning and construction funds to protect K-12 public schools against earthquake destruction came as welcome news last year. The bill’s passage followed the completion of the School Seismic Safety Project (SSSP), which provided geological and engineering assessments of 561 school buildings, and rated 93 percent of those buildings with just 1 out of 5 stars for structural safety using national seismic evaluation criteria.
The SSSP assessed approximately 14 percent of the state's more than 4,000 school buildings for grades K-12 across the state. The school selection criteria included a higher proportion of buildings constructed prior to the adoption of modern seismic standards in 1998, and those that are located in tsunami inundation zones, as identified by the Washington Geological Survey. Overall, 63 percent of the assessed buildings were found to have a "high" or "very high" seismic risks, compared with “moderate” or “lower” risks. The SSSP was conducted by the state’s Department of Natural Resource from 2017-2021, with $3.4 million from the state’s capital budget.
The School Seismic Safety Grant Program, established by the 2022 bill, is slated to provide $100 million every two years from 2023-2033 for schools facing earthquake and tsunami risks to retrofit or rebuild their schools, or construct vertical evacuation towers. Washington State lies on the Cascadia Subduction Zone, a more than 600-mile fault line with the potential to cause a 9.0 magnitude earthquake about once every 500-600 years (with its last megathrust earthquake believed to have occurred around 1700, more than 300 years ago). The state also sits on the Juan de Fuca plate and the Seattle Fault, among dozens of other known faults.
The SSSP assessments included the collection of building data by structural engineers, the collection of soil by geologists, and the provision of nonstructural safety ratings and damage estimates. Some of the highest risk buildings were studied in greater detail to generate designs and estimates for seismic retrofitting. Those estimates showed that for many buildings, preventive work would be cheaper than repairing or rebuilding after an earthquake. In addition, incorporating seismic upgrades during other school renovations can reduce the cost of seismic upgrades by 70 percent over stand-alone projects, such as those shown in the chart below, according to the SSSP.
The School Seismic Safety Project 2019–2021 Legislative Report estimates that the majority of buildings in this study would be unsafe to occupy, and half of the buildings studied would require demolition, after a “design-level earthquake” (defined as two-thirds of the magnitude of the maximum considered earthquake). Retrofitting all school buildings that face earthquake risks would be a multi-billion dollar endeavor, according to the report. The highest risk buildings are those that were made with unreinforced masonry before the 1940s, and non-ductile concrete buildings (without seismic upgrades) constructed before the mid-1970s. Secondarily, buildings that were constructed prior to 1975 out of reinforced masonry and wood frame materials are also vulnerable to collapse, according to the report. The SSSP estimates that more than 1,000 public school buildings for grades K-12 were built before 1961.
Comparing the year of construction with the risk level for 303 buildings in which information was available showed that older buildings tend to have higher seismic risk levels than buildings that were recently constructed. This sample represents 55 percent of the school buildings assessed for the SSSP. The represented buildings were assessed from 2019-2021 during the second phase of the project.
For more information on this project, visit the Github repository.