Seattle is sinking citywide, new study shows
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Seattle is sinking millimeter by millimeter, and new research shows it's more widespread — and riskier — than once suspected.
Why it matters: Land subsidence is an invisible but growing threat to urban infrastructure — cracking roads, destabilizing buildings and making low-lying areas even more flood-prone.
- In Seattle, it combines with sea level rise, seismic instability and aging buildings and infrastructure to heighten long-term risk.
Driving the news: In a peer-reviewed study published Thursday in Nature, researchers analyzed six years of satellite radar data in the 28 most populous U.S. cities.
- They found that 25 of the 28 cities are subsiding, affecting more than 33 million people — over 10% of the U.S. population — who live on sinking land.
- The cities are sinking by 2 to 10 millimeters — or 0.08 to 0.39 inches — per year, the study found.
- The new research finds that nearly 100% of Seattle's land area is sinking at measurable rates, with some zones sinking faster than others.
State of play: Subsidence has long been associated with sinking cities such as Jakarta, New Orleans and Houston — the fastest-sinking of the 28 studied — but new research shows it's a widespread issue across the U.S., including in Seattle.
- Seattle's average subsidence rate exceeds 2 millimeters per year, joining cities like New York and Chicago in the moderate-risk tier.
- In Seattle's case, tectonic activity and sediment compaction appear to be the dominant drivers — not groundwater pumping, which is a primary culprit elsewhere, per the study.
What they're saying: Researchers urge cities to factor subsidence into zoning, infrastructure upgrades and flood planning.
- They also call for long-term ground monitoring and public outreach to ensure communities are prepared for slow but damaging shifts.
Zoom in: Seattle has been planning for future sea level rise and land instability, using data from University of Washington's Climate Impacts Group, particularly in vulnerable neighborhoods such as Georgetown and South Park in the Duwamish Valley.
- The city replaced a portion of the Elliott Bay seawall with flexible foundations and underwater "marine mattresses" to absorb seismic movement and accommodate future ground shifts, including subsidence.
- To address flooding from rain and rising tides — exacerbated by subsidence — the city built a new stormwater pump station, upgraded drainage, installed grinder pumps in homes and added temporary barriers in South Park.
What's next: Mayor Bruce Harrell marked Earth Day last month by ordering a major update to Seattle's climate strategy.
- Future adaptation strategies could include zoning changes and green infrastructure as well approaches used in other areas, including raising roads or installing tide gates.
The bottom line: Uneven sinking puts stress on buildings, leading to cracks, warped frames or even structural failure, researcher Manoochehr Shirzaei told New Scientist.
- "We need to start treating subsidence like the slow-moving disaster it is."