America's Bold Plan to Earthquake-Proof San Francisco

Video narrated and hosted by Fred Mills. This video contains paid promotion for Masterworks.

SAN FRANCISCO is one of the most instantly recognisable cities in the world.

Once you catch a glimpse of the bold red paint on the iconic Golden Gate Bridge and the notorious Alcatraz Island alone in the bay, you know you couldn’t be anywhere else.

And it’s a hive, not only for tourists, but producers and directors looking for a set to shoot their next blockbuster. Well over 20 million people travel to San Francisco each year to sample its delights but dig down beneath the surface, and we're talking way, way down, and you’ll see activity’s a common theme.

This city and wider California is a hotspot for earthquakes.

Located along the West Coast of America in the Bay Area, San Francisco sits on the North American tectonic plate. It’s right on the border of the Pacific plate and divided partially by the San Andreas fault line. It’s part of an area that’s earned itself a suitably villainous nickname: the Ring of Fire.

Above: The Ring of Fire is an earthquake hotspot, seeing more seismic activity than anywhere else in the world.

More than 80% of the world’s seismic events happen along this horseshoe and if you listen to the research, you’ll know America’s West Coast could be in for another big quake in the coming years.

But how do you prepare for an event you can’t accurately predict? This is America’s bold plan to make San Francisco earthquake-proof.

San Francisco's history of earthquakes

San Francisco is no stranger to seismic activity. Aside from experiencing regular small-scale tremors, it’s had its fair share of devastating earthquakes too.

In 1989 the city was hit by a destructive magnitude 6.9 quake. More than 60 lives were lost and billions of dollars’ worth of building damage was sustained.

Turn the clocks back to 1906 and this area was recovering from an even bigger earthquake, measured at magnitude 7.9. To call it devastating would be an understatement - 80% of the city was turned to rubble or burned down, leading many people to abandon the wooden-frame construction popular across America.

Instead, they turned to concrete but that comes with its own set of problems. It’s hardy and durable but it’s not particularly ductile. If it isn’t engineered correctly to allow for some movement with ground shaking, it can become a real collapse risk during an earthquake.

If we could accurately predict when a large seismic event was going to happen, the risks to residents would be limited but it’s not quite that simple. According to the US Geological Survey, we should think of earthquake predications like weather forecasts. Outcomes are worked as probabilities, offering a percentage chance over a certain period of time.

There are a few ways we collect data to let us know what’s going on under the surface.

When working with long timescales, we know how fast the fault lines are moving, meaning geologists can go out in the field and trench fault lines. As they dig deeper, they see further back in time and in some places, can see evidence of earthquakes going back 1,000 years or more. It's why we know how often big faults rupture and cause earthquakes.

There are GPS stations attached to the ground too, which show how fast the tectonic plates are moving in relation to each other. That gives us an idea of the amount of energy that’s slowly being stored and will eventually be released. Earthquakes also tend to ‘buddy up’ and come in clusters which means keeping an eye on tremors can be pretty useful.

None of this offers guarantees because, by nature, probabilities can change but with everything we know at the moment, the USGS says there’s a 95% chance San Francisco will face a damaging earthquake in the next 100 years. There’s a 72% chance it could come in the next 30 years and measure magnitude 6.7 or more.

While that sounds like a daunting prospect, this time, the city will be better prepared.

Game-changing research

Nearly 500 miles down America’s West Coast, the University of California San Diego has one of the coolest bits of kit anywhere in the world for testing seismic resilience.

It’s called a shake table and in 2022, it underwent a $17 million upgrade. 

Above: A bird's-eye-view of UC San Diego's outdoor shake table, one of the largest anywhere in the world. 

It’s one of the largest outdoor shake tables in the world and can reproduce the full 3D ground motions that occur during an earthquake.

That means it can move in all six degrees of freedom - up, down, left to right, pitch, roll and yaw. Just like an earthquake.

It has no issues with payload either - it’s capable of carrying and shaking structures up to 2,000 metric tonnes, roughly the weight of eight Statues of Liberty.

Not only that but it can accelerate up to 4g. For context, astronauts experience a measly 3gs during a rocket launch.

To really put this table to the test, the Tallwood project was created. It’s the tallest full-scale structure ever built and tested on an earthquake simulator, and it’s made from timber.

Mass timber buildings are created by bonding layers of wood and they’re becoming ever more popular in the US. It’s not just family homes either - in 2022, California’s building code was updated to allow wood-frame high-rises.

It’s why seismic testing, like the Tallwood project, is crucial for developing structural advancements.

Standing at nearly 36 metres, it was built from cross-laminated mass timber. It incorporates a rocking wall lateral system which is basically a solid wood panel anchored to the ground with steel cables, and they contain large tension forces. Under those lateral forces, the wooden panels rock back and forth, and the cables pull the building back into place. It’s then fitted with hundreds of sensors to record performance during testing.

Above: The Tallwood project is the tallest full-scale structure ever built and tested on an earthquake simulator.

And while San Francisco did move towards concrete construction in the early 1900s, it doesn’t mean you won’t still find wood-frames. In the 1920s and ‘30s the Golden State couldn’t get enough of what were called soft-storey buildings.

Constructed over multiple floors, they’re characterised as having wood-frames, large openings for shop windows or parking on the first floor, wide doors and a lack of shear walls.

They’re not exactly shake proof.

In 2013, a law was passed to change that - "soft-storey" buildings are now required to complete retrofits. Around 6,000 have been or are being upgraded in San Francisco using technology tested and developed in locations like UC San Diego.

It’s not only soft-storeys - the city has added concrete buildings to its crosshairs. In 2024, a process began to search for structures at risk of collapse due to ground shaking. It’s called the Concrete Building Safety Program, or CBSP, and comes under the overarching earthquake safety plan.

Several of the city’s most well-known locations have already gone through a retrofit such as City Hall and the War Memorial Veterans Building.

And while that might not come cheap, it could save lives.

There are a few ways you can go about seismically retrofitting a building:

• You can beef up the structural support with steel braces and frames, columns and beams.
• Shear walls can be added between floors to absorb and distribute lateral energy.
• Push or helical piers can be added to the foundations to improve ground anchorage.
• Dampers can be fitted.
• The roof and floor diaphragms can be strengthened to improve load distribution.
• You can fit base isolators - a process in which you separate a building from the ground with shock absorbers or bearings. That allows the foundations to move while keeping the building itself secure.

Earthquake-proofing San Francisco Airport

This retrofitting process is currently taking place at one of the biggest and busiest sites in the Bay Area: San Francisco Airport (SFO).

The port’s International Terminal building is already one of the largest base-isolated structures in the world and other facilities are now in line for an upgrade.

Harvey Milk Terminal 1 reopened in 2024 following a $2.4 billion rebuild. It’s been fitted out with a range of features to make the space more modern and sustainable, alongside an extensive seismic retrofit.

It’s a process being followed at Terminal 3, where work has begun on a $2.6 billion renovation, as Derrick Homer, project manager for SFO explains:

"The seismic codes back in 1975 were significantly different than what they are today and that allows for more drift within our building structure. That means a lot more movement and so with a large earthquake, higher risk for failure or damage to the facility."

Above: San Francisco Airport has spent billions upgrading its Terminals 1 & 3, including a refreshed seismic retrofit.

As one of the Bay Area’s key travel hubs, it’s crucial not only for the airport to remain functional throughout an earthquake but it needs to keep people safe.

SFO’s Terminal 1 and Terminal 3 used what’s called a steel moment frame system but the detailing and connections weren’t up to scratch. That wasn’t the only challenge project engineers faced either.

An earthquake that hits one area could have a completely different impact if it were to happen somewhere else. For example, areas like San Francisco with deep, soft sediment experience amplified shaking.

"The airport is built on top of young bay mud that’s 100 feet deep before you get to any real bedrock. The concern during major seismic activity is liquefaction of that soil which would have further settlement and so the old terminal was really at the end of its useful life. That Terminal 1 project has been rebuilt with another steel moment frame system but it’s much more resilient now with connection details and typing."

San Francisco Airport couldn’t close for renovations. It meant building completely new structures from the ground up just wasn’t realistic. That ruled out base isolators. To add them to an existing structure, engineers would need to essentially cut all the legs loose from the buildings and put each one on a slip pad to let everything slide around.

That’s obviously tricky to achieve in a massive airport, still operating and full of people.

Instead, the steel moment frames have been given an injection of stiffness to offer long term stability.

Typically when we talk about earthquakes, we refer to them by their magnitude but engineers don’t generally see projects in the same terms. When calculating what structural methods will and won’t withstand a seismic event, it’s not necessarily ‘size’ they’re looking at. Sites are instead designed to withstand whatever the specific ground motion of an area might be, as Derrick Homer explains:

"Our team works with our geotech engineers to get soil analysis done to understand what the potential movement and acceleration of the soils in a seismic event would be. With that information the team then models out the entire structure to analyse how it performs in an event of that nature."

We can’t predict when an earthquake might happen but predicting the where is a little easier. It’s why so much money is being spent to prepare just in case. And yes, waiting for an earthquake that may or may not come sounds like a daunting prospect.

But residents can take confidence in the fact that if it does happen, San Francisco will be better prepared than ever before.


This video and article contain paid promotion for Masterworks, you can skip their waitlist here.

Video narrated and hosted by Fred Mills. Additional footage and images courtesy of UC San Diego, San Francisco International Airport, US Geological Survey, Andreas Praefcke, Warner Bros., ABC News, CBS News, University of Utah Seismograph Stations, KRON 4, SFgovTV, duncan_idaho_2007 / CC BY-SA 2.0, Europeana / CC BY-SA 3.0, Museum of New Zealand Te Papa Tongarewa / CC BY-SA 4.0, Mangoman88 / CC BY-SA 3.0, KPIX.

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