The 58 story leaning tower of San Francisco

The 58-story building has gained notoriety in recent weeks as the "leaning tower of San Francisco." But it's not just leaning. It's sinking, too. And engineers hired to assess the problem say it shows no immediate sign of stopping.

"What concerns me most is the tilting," says Buttery, 76, a retired real estate developer. "Is it safe to stay here? For how long?"

Completed seven years ago, the tower so far has sunk 16 inches into the soft soil and landfill of San Francisco's crowded financial district. But it's not sinking evenly, which has created a 2-inch tilt at the base - and a roughly 6-inch lean at the top.

The tower's troubles are apparent in its five-floor underground garage, where Porsches and Lamborghinis sit near walls bearing floor-to-ceiling cracks, many bracketed by stress gauges to measure growth.

On the sidewalks outside the Millennium Tower, engineers last month started working to figure out why the building keeps sinking and if there's a way to fix it. But the process, which involves drilling deep holes and testing soil samples, is expected to take several months.

The geotechnical engineer leading the operation, Pat Shires, said existing data indicates the tower "might" sink between 24 to 31 inches in total, but nobody knows for sure.  The lawsuits are already piling up.

So what happens if it doesn't stop sinking?  What if it clearly becomes a hazard, and everyone is required to move out?  How do you safely take down a 58 story skyscraper with a lean so extreme that no one can live there safely?

Further, San Francisco is famous for big earthquakes.  The foundation is not on bedrock, but fill.  Perhaps this effect during a large earthquake should be considered.

Further, as the building leans more and more, it's possible that instead of compression, the structure of the building might more and more become subject to shear forces?  Is the building engineered to withstand that? If so, to what extent?  What about during a significant earthquake ( 5.0 or larger)?    I'd think those parking garage cracks are a red flag of warning here.  

Finally, if the building continues to lean, as it seems everyone thinks it will, will it become a threat to neighboring areas?   Would you want to be in a building right next door is the tower is leaning your way - especially during a sharp earthquake?

We might be hearing more about this as time goes on, or, God forbid, right after a large temblor.