Engineers in San Francisco have tunnelled underground to try and understand the sinking of the 58-story Millennium Tower. Now comes an analysis from space.
The European Space Agency has released detailed data from satellite imagery that shows the skyscraper in San Francisco's financial district is continuing to sink at a steady rate - and perhaps faster than previously thought.
The luxury high-rise that opened its doors in 2009 has been dubbed the Leaning Tower of San Francisco. It has sunk about 40 centimetres into landfill and is tilting several inches to the northwest.
A dispute over the building's construction in the seismically active city has spurred numerous lawsuits involving the developer, the city and owners of its multimillion dollar apartments.
Engineers have estimated the building is sinking at a rate of about 2.5cm per year. The Sentinel-1 twin satellites show almost double that rate based on data collected from April 2015 to September 2016.
The satellite data shows the Millennium Tower sunk 40 to 45 mm over a recent one-year period and almost double that amount - 70 to 75 mm over its 17-month observation period, said Petar Marinkovic, founder and chief scientist of PPO Labs which analysed the satellite's radar imagery for the ESA along with Norway-based research institute Norut.
"What can be concluded from our data, is that the Millennium Tower is sinking at a steady rate," Marinkovic said in a telephone interview from The Hague, Netherlands.
The Sentinel-1 study is not focused on the Millennium Tower but is part of a larger mission by the European Space Agency tracking urban ground movement around the world, and particularly subsidence "hotspots" in Europe.
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