Over two dozen of the largest cities in the United States are experiencing subsidence, posing risks to thousands of buildings and millions of residents. Seattle is among those cities grappling with this issue.
In response to the challenges posed by rising sea levels and land instability, Seattle has been proactive in its planning efforts. Utilizing data from the University of Washington’s Climate Impacts Group, the city is particularly focused on vulnerable areas such as Georgetown and South Park in the Duwamish Valley.
While the sinking problem has been previously documented, recent advancements in satellite technology have allowed scientists to more accurately measure subsidence. By sending radar signals towards the Earth’s surface and timing their return, researchers have determined that 25 of the 28 largest cities in the country are affected.
Among these cities, Fort Worth, Houston, and Dallas have the highest rates of subsidence, exceeding an average of 4 millimeters per year. In comparison, Seattle, New York, Chicago, Columbus, and Denver experience average subsidence rates of over 2 millimeters annually.
The primary cause of this subsidence is often groundwater extraction; however, in cities like New York, Philadelphia, and Washington D.C., it is mainly attributed to “glacial isostatic adjustment.” In Seattle, Portland, and San Francisco, tectonic activity is likely the leading factor. In Seattle, this tectonic movement, combined with rising sea levels, seismic instability, and aging infrastructure, increases long-term risks.
Seattle’s average subsidence rate exceeds 2 millimeters per year, placing it in a moderate-risk category alongside cities like New York and Chicago. Importantly, the study indicates that in Seattle, tectonic forces and sediment compaction are the primary drivers of subsidence, rather than groundwater pumping, which is a significant factor in other regions.
