- San Francisco is undergoing a building boom.
- But the city is at serious risk for a major earthquake. And the building codes for skyscrapers aren’t strong enough, according to experts.
- The next big Bay Area earthquake could be disastrous.
San Francisco is undergoing a skyscraper building boom, but the city’s building stock – including skyscrapers – is at serious risk in a major earthquake.
There’s a 76% chance that the San Francisco Bay Area could experience a devastating 7.2 magnitude earthquake within the next 30 years, according to some reports. The earthquake that caused the fire that leveled much of the city in 1906 was measured at a magnitude of 7.9.
In downtown San Francisco, where most of the new skyscrapers are clustered, a 7.2 magnitude quake could leave nearly 30% of apartments or office spaces in the neighbourhood completely unusable. That’s almost one in three residences.
The city is located directly above a group of major, active fault lines, including the San Andreas and Hayward faults. Residents of the Bay Area are used to small tremors and shakes, but a large magnitude earthquake could be disastrous – and the recent skyscraper boom is making the situation even more dangerous.
According to a New York Times investigation, the area under San Francisco’s downtown – near the notorious Millennium Tower, which has sunk 17 inches and tilted 14 inches since it was completed in 2008 – has a high risk of “liquefaction,” or acting like quicksand, in the event of a major earthquake.
Beyond liquefaction, a number of San Francisco’s most prominent skyscrapers – home to hotels, office buildings, and apartments – are potentially vulnerable to earthquakes because of a defect in their construction.
A recent report from the USGS identified 40 steel-frame skyscrapers, built between 1960 and 1994 clustered in downtown San Francisco, reports The New York Times.
The steel frames used in the buildings’ construction can be easily fractured by earthquake-related shaking, causing severe damage to the buildings. While the building code was rewritten in 1994 to correct the flaw in the steel frame-construction, most of the buildings have not yet been retrofitted, according to The Times.
That hasn’t stopped construction in the area. The Salesforce Tower, which opened earlier this year in downtown San Francisco, is the tallest building west of the Mississippi River, and there are more than a dozen buildings over 240 feet tall that are planned, The Times reports.
San Francisco’s building code does not accurately account for the risks of the city’s underlying geology. Buildings must be designed to have a 90% chance of avoiding total collapse in the event of an earthquake, according to the Times.
The risk is magnified not only for people in a tall skyscraper but for the area around it when a building collapse causes an avalanche of debris.
While the state of California has strict measures to protect schools and hospitals from collapsing in the event of an earthquake, skyscrapers don’t. A five-story building has the same requirements as a 50-story building.
“I don’t understand why that’s acceptable,” Lucy Jones, a former geologist at the USGS told The New York Times. “Enough buildings will be so badly damaged that people are going to find it too hard to live in L.A. or San Francisco.”
San Francisco is justifiably building many of these skyscrapers in an attempt to alleviate pressure on housing costs in the city, as well as to provide office space for the city’s omnipresent tech industry. But experts say building engineers aren’t doing enough to prepare for high-magnitude quakes.
“It’s kind of like getting in a new aeroplane that’s only been designed on paper but nobody has ever flown in it,” Thomas H. Heaton, the director of the Earthquake Engineering Research Laboratory at the California Institute of Technology, told The Times.
Beyond earthquakes, the Bay Area is a geologic nightmare for a number of other reasons. Sea level rise is threatening to wipe out some of the city’s most valuable real estate, and more frequent storms can compound the risk of flooding in the city.
On top of that, the city, which is built over layers of unstable mud, clay, and landfill, is actually sinking into the Pacific Ocean in a process geologists call “subsidence.”
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