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28 Years After Loma Prieta: Is The Bay Area Ready For ‘The Big One’?

Nearly 30 years ago, San Francisco faced one of the biggest natural disasters in its history. The Loma Prieta earthquake had struck, buildings were destroyed and vulnerabilities were revealed. Years later, the Bay Area is building better buildings based on lessons learned, but while some buildings are ready for "The Big One" others still have a long way to go.

A building that collapsed in the Marina District of San Francisco during the 1989 Loma Prieta earthquake

It was 5:04 p.m. on Oct. 17, 1989. The Oakland A’s and San Francisco Giants were warming up before the third game of the World Series. Two local teams had made it to the biggest baseball showdown of the year, and many baseball fans were anticipating another installment of the Battle of the Bay. Instead of watching what was likely to be a great game, something unexpected happened. The ground began to shake.

Cameras at Candlestick Park swayed and flickered and then went out. They had just broadcast an earthquake for the first time on live television. When the shaking stopped, ballplayers, announcers and onlookers were visibly stunned.

A magnitude 6.9 earthquake had hit the Bay Area, the largest earthquake to hit the region since 1906. A freeway collapsed, as did part of the Bay Bridge’s upper deck. Several buildings, many of which were in the Marina District, sustained heavy damage. The earthquake resulted in $5B worth of damage and killed 67 people.

It has been nearly 30 years since the Loma Prieta earthquake, which geologists call moderate. The region is overdue for an earthquake of greater strength that could equal the 7.8 magnitude 1906 earthquake, which almost destroyed San Francisco.

The Pending Disaster

U.S. Geological Survey earthquake geologist David Schwartz assesses cracks in the asphalt parking lot near the Hayward Fault. The cracks show creep, which is characteristic of movement of the Hayward Fault.

“You have a fault like Hayward that passes through the most urbanized and most densely populated part of the Bay Area,” U.S. Geological Survey earthquake geologist David Schwartz said.

The Bay Area’s population has grown by 1 million in the last 30 years and over 7.6 million people live in the region. By 2030, San Francisco’s population is expected to reach 1 million, and the Bay Area is expected to reach a population of 9 million by 2040.

A significant earthquake could cause hundreds of billions of dollars in damage to Bay Area infrastructure and buildings. Many of the new buildings added to the Bay Area since Loma Prieta are safer and will be resilient against earthquakes, but older building stock is the Bay Area’s biggest risk since it was built long before current seismic standards.

The Bay Area has about 89M SF of office worth over $35B, according to data from Transwestern. Another 131M SF of industrial worth $15B and 60M SF of retail worth over $13B exists in the Bay Area. About 85,000 buildings, or 1.4B SF, were built before 1990 and 700 buildings of about 41M SF have still not been renovated.

Housing would be hit the hardest, especially low-income and affordable housing, which is often rebuilt as market-rate housing after a disaster, according to a report from the Association of Bay Area Governments. Over 150,000 housing units would be potentially lost during a major earthquake.


And it is not just the Hayward Fault that could be problematic. There is the Rogers Creek Fault, the continuation of the Hayward Fault system north into Santa Rosa. There is the Calaveras Fault in Danville. The Concord Fault goes through the middle of downtown Concord. Plus, there is the San Andreas fault, which spans from Southern to Northern California. There are eight discovered major fault lines throughout the Bay Area that could cause a significant earthquake, according to the USGS.

“The Bay Area is positioned in the middle of the boundary zone of the North American plate and Pacific plate,” Schwartz said. “The Bay Area has the highest density of faults per square mile in any urban center.”

The Loma Prieta earthquake broke a long period of quiet following 1906. The 1906 earthquake was so powerful, it broke the Earth’s crust for 300 miles.

“It was basically popping a balloon, but rather than letting the air out slowly, all the stress was relaxed on the crust throughout Northern California,” Schwartz said.

Since 1906, the region has had an unusually small amount of earthquake activity. Research has shown that from the late 1600s to about the 1790s, every major fault in the Bay Area produced a large earthquake cluster, according the Schwartz. 

“I think to a degree we’re on borrowed time,” Schwartz said.

A timeline of earthquakes in the San Francisco Bay Area

He said there is a 72% chance in the next 30 years of some large earthquake happening along a Bay Area fault and if it happens close to the crust, it could be much worse than the Loma Prieta earthquake. The Loma Prieta earthquake did not cause as much damage as it could have because it was 70 miles south of Oakland and the quake did not strike the state’s largest fault, the San Andreas.

“All of these faults haven’t moved in quite a while and have to catch up,” Schwartz said. “I think in all probabilities … down the road almost inevitably faults will begin to move again.”

The Hayward fault has a 31% chance of causing a 6.7 or greater earthquake in the next 30 years while the Northern part of the San Andreas fault has a 33% chance of causing a strong earthquake, according to UC Berkeley External Relations Officer, Berkeley Seismology Lab Jennifer Strauss.

To better prepare the state and the region, the USGS and UC Berkeley have been working on an earthquake warning system that can provide a few seconds up to three minutes of warning for an earthquake. This would be enough time to stop trains, prepare first responders and inform building managers to stop elevators and warn tenants and employees.

When an earthquake strikes, it sends out initial P-waves, which would set off a seismograph. The Shake Alert system would detect those waves and send out a signal to groups like PG&E or any other groups connected to the system, according to the USGS’ Schwartz. The system can warn people about the strength of the earthquake as well.

The system is in test mode and will start to roll out on a limited regional basis by the end of next year.

“It’s not a prevention for all things bad,” UC Berkeley’s Strauss said. “You still need well-built buildings, public utilities and things like that. It is a tool in a toolkit of information.”

What Loma Prieta Taught Us

A soft-story building near Beach and Divisadero streets in San Francisco that was damaged during the Loma Prieta earthquake

Loma Prieta was a wake-up call for the region. Soft-story buildings in the Marina District collapsed, causing significant damage. These buildings are built over a parking podium and revealed a vulnerability previously unknown.

“Humankind thinks we rule the Earth,” Transwestern Capital Markets Senior Vice President Michael Federle said. “But when freeways and buildings start to fall over, it makes you think twice. All kinds of things you thought were solid are reduced to rubble in an instance."

Over 17,000 buildings in the Bay Area have been designated as soft-story. These buildings account for over 112,000 housing units, according to the Association of Bay Area Governments.

Since Loma Prieta, building codes have changed and San Francisco has mandated that soft-story buildings, like the ones that collapsed in the Marina District, be retrofitted. But much more needs to be done. Over 1,100 building owners in San Francisco had yet to take the initial steps to comply with San Francisco’s seismic safety standards in September. Oakland also has a soft-story risk, but does not have similar standards as San Francisco.

In the Sunset District, homes are built on sand dunes and the Marina District was built on top of a landfill from the Pacific Exposition years before and was not stable fill, according to Federle. Both areas are susceptible to liquefaction, when the soil turns into quicksand during an earthquake.

“There have been major improvements in construction for multifamily and commercial properties in general, but that doesn’t mean there aren’t homes that could be retrofitted and upgraded to meet codes,” Federle said.

Commercial buildings have made the most significant strides. Jay Paul Co.’s 181 Fremont is one of the most resilient buildings added to Downtown San Francisco in recent years. Hospitals also have undergone significant renovations since the Northridge earthquake in 1994 after hospitals sustained $3B in damages. As of 2016, over 90% of acute care hospitals in the state were no longer at risk of collapse. Many have used required seismic upgrades as a way to rebuild hospitals up to current codes and add additional facilities.

Fixing Vulnerabilities

California Earthquake Authority Chief Mitigation Officer Janiele Maffei

Thousands of buildings throughout the Bay Area still need to be retrofitted and 1.2 million homes statewide are vulnerable to collapse during a major earthquake, according to California Earthquake Authority Chief Mitigation Officer Janiele Maffei.

The CEA is helping fill the gaps in retrofitting older homes and small apartment buildings with up to four units. As part of its Earthquake Brace and Bolt program, CEA is offering $3K toward retrofitting homes built before 1979 with a crawl space under the first floor, according to Maffei. These crawl spaces are not bolted to the foundation and create a vulnerability for the home to slide or topple off the foundation.

Fewer than 10% of Californians have earthquake insurance, meaning home repairs would come out of their pockets. Renters, too, would be at risk since earthquake insurance includes loss of use and provides funds for new housing while an apartment is being repaired.

“The Bay Area has done a tremendous amount for public structures, BART, Caltrain, East Bay MUD,” Maffei said. “Where we really need to focus is privately owned buildings.”

Strengthening homes and apartment buildings is critical to keeping residents, especially renters, in the Bay Area after a disaster.

“In the Bay Area, more than 50% of the population is renters,” Maffei said. “If we lose a lot of housing, we will lose a lot of our workforce.”

An Earthquake Would Damage More Than Just Buildings

Bay Area Council Senior Vice President of Government Relations Matt Regan
at Levi Stadium in Santa Clara

With over 100,000 housing units potentially offline after an earthquake there could be catastrophic consequences to the Bay Area.

Even a disaster like the North Bay wildfires has created an unexpected need for over 5,000 housing units that the Bay Area simply cannot absorb, Bay Area Council Senior Vice President of Public Policy Matt Regan said.

Low-income populations and the elderly will be particularly at risk since they may not have the means or ability to find housing that fits their socioeconomic needs. If residents are unable to stay in their homes after a disaster, they cannot participate in rebuilding the economy and their communities, according to the Association of Bay Area Governments.

“If we can’t accommodate the North Bay fires, we certainly can’t accommodate an earthquake,” he said. “The disaster will not last for 10 seconds. It will go on for years because so many people will be forced out of the Bay Area.”

CORRECTION, OCT. 17, 2:53 P.M. PT: A previous version of this story did not have the right age for homes covered through the state's Earthquake Brace and Bolt program. The program applies to homes built before 1979. The story has been updated.