1989 Loma Prieta temblor shook up need for earthquake solutions

1989 Loma Prieta temblor shook up need for earthquake solutions

A quarter-century has passed since a violent earthly shift in the Santa Cruz Mountains set off a chain of calamity some 60 miles north in San Francisco and Oakland, where busy roads and bridges failed, homes and businesses were damaged or toppled, and gas lines ruptured to cause raging fires across The City's Marina district.

As much of the nation watched the 6.9-magnitude Loma Prieta earthquake's devastation play out on television, rescue workers found 63 people dead and nearly 4,000 injured. Damage estimates ranged from $6 billion to $8 billion. It was easily the country's most televised natural disaster to that point, with attention initially sparked when Game 3 of the World Series between the Giants and A's at Candlestick Park was abruptly canceled just before first pitch and then delayed for more than a week.

Even to a region known for major seismic activity, the sheer size of the Bay Area's largest earthquake since 1906 caught most residents off-guard.

The toll of the disaster was stark, but advancements did arise from the tragedy and chaos of 1989 — stricter new building standards and required fixes for existing structures, a new dedication to scientific understanding of the areas at risk, the emergence of a short-term warning system and the development of computer-generated shake maps for emergency officials to have a much quicker understanding of where help is most needed in the immediate aftermath.

“A lot has changed in terms of what we know and when we know it,” said Brad Aagaard, a research geophysicist with the U.S. Geological Survey. “We can detect an earthquake within seconds. Within minutes, we can create maps of the shaking, and we can follow that up with estimates of fatalities and economic losses. Back then, we didn't have tools to tell the distribution of shaking, the number of people affected, the overall impact.”


The first major test of the relatively new ShakeAlert early-warning system developed by UC Berkeley's Seismological Laboratory came less than two months ago during the 6.0-magnitude quake in Napa County.

For all intents and purposes, it worked — as in, it provided five to 10 seconds of forewarning in some areas. Through a network of seismic-wave sensors placed near fault lines, the system is generally able to give lead time of about five to 20 seconds, but perhaps up to one minute of warning before the ground starts to shake, depending on the proximity from the epicenter.

One of the region's first uses of the technology as a warning system actually came about in 1989 when scientists placed a radio seismic-wave sensor near the Loma Prieta epicenter to detect aftershocks and quickly alert workers who were clearing rubble from Oakland's collapsed Cypress Street Viaduct section of Interstate 880, which was the site of the majority of the disaster's deaths.

While seismic waves can travel at hundreds or thousands of miles per hour, depending on ground depth, a well-placed sensor can send a warning even faster, giving people a few crucial moments to take cover and providing the potential for automated reaction from critical infrastructure equipment like transit trains, hospitals and fire departments. Earthquake-prone countries like Japan and Mexico already have some version of such public systems in place.

The Napa quake warning in August was available only to less than 200 prototype users and emergency officials, and the general public has yet to gain access.

“Napa was a wake-up call in the sense that it was the biggest earthquake that could happen without terrible damage death,” said Jennifer Strauss, a spokeswoman for the Berkeley lab. “The big thing is getting more sensors in the ground so the warning can be faster and more reliable.”

Strauss said a smartphone app connected to ShakeAlert also is in the works, and that household earthquake alert receivers similar to smoke alarms could provide a more universal warning.

“Everything is on the table — special devices for your house, cellphones, PA systems for schools, automated controls,” Strauss said. “If people like this idea, we could use their support and advocacy.”

Still, even though BART trains were not running when the Napa quake hit at about 3:30 a.m., the transit agency received a 10-second warning from ShakeAlert. Had BART been active, trains traveling less than 30 mph would have been stopped and faster-moving trains would have been slowed down.

A joint effort between UC Berkeley, the University of Washington and the USGS, among others, is underway to create a unified West Coast early-warning system, although the various estimates of $40 million to $80 million needed to get it running, and the annual $12 million to $16 million for maintenance, have yet to be funded at the state or federal level. California lawmakers passed a bill last year establishing the need to build an early-warning system for the public, but the legislation did not dedicate funding.


A private company called Seismic Warning Systems is advocating a private-public partnership, and contends that method could more quickly deploy subscription-based sensor networks like ones already being used in Southern California. The Scotts Valley-based company says the system overseen by “academic research communities” is too slow and incomplete, and the firm boasts the recent performance of its QuakeGuard system in Vallejo. It was used to automatically open fire department garages to prevent potential door jams during the Napa quake.

Scott Nebenzahl, the company's director of government affairs, says the ShakeAlert system also could have an unfortunate “blind zone” of transmission delay that could cost precious seconds.

“The goal of an earthquake warning system should be to reduce the threat to life and infrastructure and property, with warning delivered within milliseconds,” Nebenzahl said.

But the idea of a subscription-based system doesn't sit well with advocates of ShakeAlert.

“Earthquake early warning should be available to everyone,” Strauss said. “It shouldn't be a proprietary thing.”

Those most familiar with seismic threats to the region hope to have a system in place prior to the so-called Big One — an inevitable earthquake of 8.0 magnitude or greater, likely to cause widespread death and hundreds of billions in damage. San Francisco's 1906 earthquake was a 7.8-magnitude event, and even though building standards have been updated to better withstand shaking, any high-magnitude temblor could take out bridges and BART trains, and temporarily liquefy the ground under buildings to create previously unseen catastrophe in The City.

For the relatively more frequent 6.0 events like in Napa, the colored topographical relief-style shake maps created by ShakeAlert could also help scientists learn more about what movement on particular faults does to the landscape and infrastructure.

“There are minor structures that haven't received a lot of attention, maybe a small bridge or overpass,” said Thomas Holzer, a USGS research geologist. “Roads locally can be on bad soils where you might get liquefaction. The advent of digital instruments can provide a much clearer picture of earthquakes after the fact.”


The fledgling warning system should not be confused with any kind of reliable long-term accurate earthquake prediction, which is considered by most geologists to be impossible with current information and technology. While scientists continue to investigate Bay Area problem spots like the San Andreas fault that sparked Loma Prieta, and give more attention to the Hayward fault that cuts through the base of the East Bay hills, any predictions have remained limited to providing a vague probability of whether a fault will slip over a period of multiple decades. And even if an early-warning system is comprehensively deployed on the West Coast, there likely still won't be much notice for those unfortunate enough to be near the epicenter.

“It's difficult to get a warning fast enough to the people who are feeling the strongest shaking,” Aagaard said. “On a person-by-person level, you still have to be prepared for an earthquake.”

Decades later, quake safety upgrades still a focus for SF

The Loma Prieta earthquake's legacy is still shaping the landscape of The City 25 years later.

A major policy push just before the 1989 disaster revolved around unreinforced masonry — basically chimneys and other brick structures that were not held up by a building's primary beams.

Thanks to a 1986 state law, more than 2,000 such buildings have been updated in San Francisco.

Last year, Mayor Ed Lee pushed through a city law to require major retrofitting upgrades to so-called soft-story structures, defined as multistory buildings having a ground floor with a garage, large windows or other openings. The law covers buildings that are at least three stories tall with five or more dwelling units. The move was aimed at avoiding building collapses like the several that occurred in the Marina in 1989.

According to The City's Department of Building Inspection, more than 6,000 building owners were identified as having a soft-story property covered by the law. After the deadline passed in September, only 400 notices had not garnered responses. From those owners who did respond, the DBI determined that 4,800 buildings still need some type of work. The City had previously pushed a voluntary soft-story retrofit program that elicited only 50 upgrades.

When the San Francisco law was adopted in April of last year, retrofit costs were estimated at $60,000 to $130,000 per building. Bill Strawn, a DBI spokesman, said many of the structures with issues were built in the 1930s and 1940s, and that buildings constructed since 1973 are better off due to major changes in San Francisco building codes mandated by state law following the devastating 1971 San Fernando earthquake in Southern California.

Strawn said it's a challenge to keep The City's buildings earthquake-resistant but that serious progress has been made over the past quarter century.

“Whereas in 1989, one in four of these types of buildings were expected to collapse, it's down to about one in 30 now,” Strawn said.

Loma Prieta's toll


Seconds of shaking


Magnitude of earthquake


Deaths from Santa Cruz County to Bay Area


Injuries from Santa Cruz County to Bay Area

$6B to $8B

Total property damage

Source: U.S. Geological Survey

Bay Area NewsEarthquakeLoma Prieta Earthquakeseismic safety

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