‘Leaning tower’ isn’t a moniker most people want attached to an inhabited skyscraper, but that’s what people are calling the 58-story Millennium Tower in San Francisco. And for good reason. The European Space Agency recently unveiled (ESA) satellite data which shows not only that the tower is leaning, but it’s sinking – and a lot faster than engineers previously thought.

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ESA’s Sentinel-1 satellites gathered the data showing the tower filled with luxury condominiums is sinking at a rate of around two inches each year. According to KTVU, that number is about twice what engineers expected. The Millennium Tower has sunk 16 inches since it opened in 2009.

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Why is the tower sinking? Although ESA says the exact cause is not yet known for sure, “it is believed that the movements are connected to the supporting piles not firmly resting on bedrock.”

ESA scientists could see the tower’s movement through combining several radar scans from the satellites. According to ESA, “The technique works well with buildings because they better reflect the radar beam.”

The scientists could map other areas in the Bay Area using the satellite data. They saw some buildings were moving along the Hayward Fault, and even noticed an uplift of land near Pleasanton. They think replenished groundwater may have resulted in the uplift. The San Francisco information will benefit researchers as they scrutinize subsidence in other cities of the world.

Millennium Tower developers say it’s safe for inhabitants to stay in the leaning tower. But earlier in November, San Francisco City Attorney Dennis Herrera filed a lawsuit against developers as they did not tell buyers the tower is sinking “much faster than expected.”

Via KTVU

Images via Wikimedia Commons and Copernicus Sentinel data (2015-16)/ESA SEOM INSARAP study/PPO.labs/Norut/NGU