European satellites show San Francisco tower is sinking 2 inches a year

As lines form in a major legal battle over a sinking and tilting luxury tower in San Francisco, the European Space Agency (ESA) has waded in by saying its satellite images show the building is experiencing vertical subsidence of nearly 2 inches each year.

We are not going to sit by and allow a developer to enrich themselves at the expensive of others by hiding crucial information– Dennis Herrera, San Francisco City Attorney

Data from the ESA’s Sentinel-1 satellites acquired between 22 February 2015 and 20 September 2016 show that the controversial Millennium Tower is sinking by about 40mm (1.57 inches) a year in the "line of sight" – that is, the direction that the satellite is "looking" at the building – which the ESA said translates into a vertical subsidence of almost 50mm (1.96 inches) a year, assuming no tilting.

The ESA, working with Norwegian scientists, hoped to demonstrate the value of the technology as a way of monitoring land deformation, but it is commenting on a matter that is the subject of multi-directional and potentially high-stakes legal battle.

Its revelation followed a lawsuit filed earlier this month by San Francisco’s City Attorney against the tower’s developer, alleging the developer knew the 58-storey building was sinking further and faster than expected, but did not tell potential home buyers as required by law.

The issue came to a head in August after it emerged that the luxury apartment building at 301 Mission Street had sunk 16 inches since it was finished in 2008, and was leaning, according to reports, by as much as 7.6 inches off the vertical at the tower’s top.

The City Attorney’s Office claims the developer, Mission Street Development LLC, knew by February 2009, before any units were sold, that six inches was the maximum amount of settlement predicted for the tower by the project’s geotechnical engineer, but that by the time the tower was completed in or around February 2008, it had already settled almost 6 inches.

A year later, by February 2009, the Tower had settled 8.3 inches, alleged the City Attorney, Dennis Herrera.

"We are not going to sit by and allow a developer – or anyone else – to enrich themselves at the expensive of others by hiding crucial information that they’re required by law to disclose," Herrera said. "That gave the developer an unfair advantage against competitors, and it cheated homebuyers out of information they needed to make an informed decision."

He added: "Before they had sold a single condo, Mission Street Development LLC knew their building had sunk more than it was supposed to in its lifetime – and that it was still sinking. Yet they didn’t tell the home buyers as they’re required to do so under the law. It’s that simple."

The developer, Mission Street Development LLC, disagrees.

A spokesman told the New York Times that Herrera’s allegations had "no merit", and repeated the developer’s previous claim that the tower’s subsidence was caused by de-watering from a major excavation at a neighbouring construction site, where the city’s Transbay Joint Powers Authority (TJPA) is constructing a large transit hub.

A number of Millennium Tower condo owners have sued the TJPA and it members, including the City and County of San Francisco.

For its part, the TJPA has argued that the subsidence of Millennium Tower, one of the heaviest buildings in the area and built on reclaimed land, is caused by inadequate foundations, and began before de-watering started.

For more on this story, see:

• Residents’ alarm as heavy luxury tower in San Francisco sinks and tilts

Image: Data from the Sentinel-1 satellites acquired between 22 February 2015 and 20 September 2016 show that Millennium Tower in San Francisco is sinking by about 40 mm a year in the "line of sight". The colour scale ranges from 40 mm a year away from radar (red) to 40 mm a year towards radar (blue). Green represents stable targets (ESA)