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San Francisco Seismic Risk

San Francisco Building Collapse

San Francisco is no stranger to massive earthquakes. In 1906 the city experienced one of the most significant earthquakes in history, destroying most of its downtown structures and killing an estimated 3,000 people. Since then the expectation has been that San Francisco learned from the loss. That it embraced the likelihood of another large earthquake and turned its focus toward ensuring the damage would never again reach the levels it did that day in 1906.

A recent scientific investigations report conducted by the United States Geological Survey (USGS), however, contains information alarming to Bay Area residents: Almost 40 high rise-buildings—some with more than 15,000 visitors each day and others operating as busy hotels—may be in danger of collapse if another big earthquake occurs near the city. The buildings, which researchers identified in an appendix of the USGS report, were constructed with a defect in their steel frames that makes them more susceptible to collapse. Such collapses can be devastating to people in or near the buildings.

Residents and legislators are now pushing city officials to identify which buildings carry the greatest risk and to pursue retrofits for those buildings.

Almost 40 San Francisco High-Rises at Risk of Collapse in the Event of an Earthquake

The USGS report was not intended to be about the 39 vulnerable high rises in San Francisco. It instead focused on the potential outcome of another large-scale earthquake like those that occurred in 1906 and 1989 (magnitude 7.8 and 6.9, respectively). The report is titled “The HayWired Earthquake Scenario—Engineering Implications” in reference to the Hayward Fault that ruptured in 1868 and is expected to do so again.

It was only after Thomas Fuller, a reporter for The New York Times, noticed the list of faulty-construction high rises in the appendix and wrote an article on them for the paper that the new focus came to light.

The high rises in question were built between 1960 and 1994 when engineers used an (unbeknownst to them) flawed construction technique in some steel-frame buildings. The engineers welded the columns and beams of these buildings together, instead of using bolts and rivets as in the past. This was a cost-conscious move and one that expedited the construction process, but it also made buildings that were overly flexible and could sway dangerously in certain situations. By the mid-1980s, officials changed building codes to ensure buildings were less flexible and in the 1990s the welding technique itself was changed. By then, however, the San Francisco skyline was dotted with buildings constructed with the faulty method.

The risks created by the flawed construction technique are only relevant in the face of an extreme earthquake, experts say, but San Francisco is a place where extreme earthquakes aren’t uncommon. Unlike some southern California cities, however, San Francisco hasn’t ordered mandatory retrofits of these buildings.

Keith Porter is an earthquake engineering expert and worked as a lead on the USGS report. He spoke with the Times about the lack of attention given to the problem.

“This is an issue that structural engineers should have been dealing with continuously since the mid-1990s and we just dropped,” Porter said. “We don’t know how to deal with a problem this big.”

Some Buildings Have Since Been Retrofitted, But Costs Are Steep

The 39 high rise buildings mentioned in the USGS report are scattered throughout the city and are familiar names to Bay Area residents. There are the Transamerica Pyramid and the San Francisco Marriott; the Salesforce West building and the headquarters of Pacific Gas and Electric. There’s even the building where The New York Times has its San Francisco bureau, which also happens to be where Fuller was working on the article about the risky buildings when, ironically, a 3.7 magnitude earthquake shook the building.

The owners of some of the buildings on the list have retrofitted them. The Hilton San Francisco Hotel opted to retrofit in 2012 and the California Automobile Association Building is also up to current building code. The impetus for the latter change wasn’t entirely safety, though. The building’s owners wanted to convert it from office to residential and were required to do the retrofit in the process. A principle with Emerald Fund, who co-owns the building, told the Times that he doubted that owners would retrofit their buildings for safety without being required to because of the extensive time and money it takes. At the California Automobile Association Building, it took a year and more than $20 million to complete.

Experts Say Devastating Earthquake in Northern California is Only a Matter of Time

Uncertainty is everything where earthquakes are concerned. Experts can study their originations and their patterns, but they can’t be predicted. One thing that is largely agreed upon, however, is that one day San Francisco will experience another high-magnitude quake.

San Francisco is believed to have soft soil, which amplifies ground shaking, and was a factor in the intensity of its two largest earthquakes. The city sits along the San Andreas Fault line and near the Hayward Fault line, exposing it to some of the most concerning seismic areas. It would also fit past averages for another major earthquake to occur soon. Researchers studying the Hayward Fault found that the 12 most recent major earthquakes to occur there happened in approximately 150-year intervals, and while earthquakes are unpredictable, it’s been 150 years since the last major one on the fault.

Some researchers say that, based on current models, there is an approximately 75 percent chance of at least a magnitude 7 earthquake taking place in both Northern and Southern California within 30 years. This means that while San Francisco’s faulty buildings may not seem urgent to the average resident, there could well be a looming deadline to get them fixed.

Bill Proposed to Map Seismically Vulnerable Buildings in California

Adrin Nazarian, an Assembly member representing the 46th Assembly District, introduced legislation containing two bills aimed at minimizing damage in the event of a major earthquake. One of the bills seeks to strengthen building codes in hopes of keeping buildings from being uninhabitable after such a seismic event. The other bill seeks to identify and map vulnerable buildings.

Through the second bill, Nazarian says residents would gain important awareness about the buildings they live in and frequent so that they could make informed decisions about their personal safety. It would also give California officials a better understanding of areas where they need to move quickly on retrofits.

The bill has made it through seven committees and is now waiting in the Senate Appropriations Committee.



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