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Seismologists Warn of Looming Quake on Hayward Fault

By Riya Bhattacharjee
Tuesday December 18, 2007

When geologists across the country observe the 140th anniversary of the 1868 Hayward earthquake next year on Oct. 21, they will have more than speeches and slideshows on their mind. 

Seismologists at the American Geological Union’s meeting at the Moscone Center in San Francisco last week warned that the average interval between the past five earthquakes on the Hayward Fault was 140 years. 

“The 1868 earthquake was the first great ‘San Francisco earthquake,’ and one of the most destructive earthquakes in the nation’s history,” said Arthur Rodgers, a seismologist at the Lawrence Livermore National Laboratory (LLNL). 

“However it has always been eclipsed by the great 1906 quake. It’s important to know that if an earthquake of the same scale happens today on the Hayward Fault, its aftereffects will be devastating.” 

Rodgers, along with Xiao-Bi Xie from the Institute of Geophysics and Planetary Physics at UC Santa Cruz and Anders Petersson from LLNL performed simulations of the 1995 Kobe earthquake on the Hayward Fault using reported finite rupture models from large strike-slip earthquakes under the auspices of the U.S. Department of Energy at Livermore lab. 

“We wanted to calculate what the ground motions will be on a large earthquake on the Hayward Fault,” Rodgers said. “The results showed large damaging ground motion levels near the asperities along the fault. Very strong ground motions are predicted in the sedimentary basins, particularly the Evergreen, Cupertino, San Leandro, Livermore basins and San Pablo Bay. Moderate damage will also occur in Berkeley and Oakland.” 

The 1868 earthquake—which took place at 7:53 a.m. with a magnitude of 7 on the Hayward Fault—stands as the country’s 12th deadliest quake. 

The last of a decade-long sequence of earthquakes in the Bay Area, the Hayward Earthquake left 30 people dead and brought about an extensive loss of property. 

According to a U.S. Geological Survey (USGS) report, the damage was most severe in Hayward and the nearby towns of Alameda County. A town of about 500 residents back then, Hayward had almost every building either damaged or extensively wrecked.  

San Leandro—with a population then of about 400—saw the second floor of the Alameda County courthouse collapse and other buildings destroyed. 

Oakland, then a town of about 12,000 with predominantly wood frame buildings, sustained far less damage than either Hayward or San Leandro. 

San Francisco, which was then the largest U.S. city on the West Coast with a population of 150,000, suffered damages to the Custom House and several other structures built on landfill reclaimed from the former Yerba Buena Cove (modern day Financial District). 

The USGS report states that very little information is available on the 1868 earthquake because of a lack of funding from the state and the non-existence of seismographs during that time. 

“The 1868 Hayward earthquake and more recent analogs such as the 1995 Kobe earthquake are stark reminders of the awesome energy waiting to be released from below the east side of the San Francisco Bay along the Hayward Fault,” said Tom Brocher, a seismologist with the USGS and one of the authors of the study, “The M7 Oct. 21, 1868 Hayward Earthquake, Northern California—140 Years Later.” 

“The population at risk from a Hayward Fault earthquake is now 100 times larger than in 1868,” Brocher said. “The infrastructure in the San Francisco Bay Area has been tested only by the relatively remote 1989 magnitude 6.9 Loma Prieta earthquake ... We are not saying that an earthquake is going to happen next year but if it does, we are not going to have any warnings. We have to prepare now. Whatever we have during the quake, we will have the same during the next three days.” 

To help attract public attention to future hazards, the 1868 Hayward Earthquake Alliance ( was formed.  

Consisting of public and private sector agencies and corporations, the alliance has planned a series of activities including public forums, conferences and commemorative events leading up to the 140th anniversary. 

Labeled “a tectonic time-bomb” by USGS geologist David Schwartz, the Hayward Fault is the single most urbanized earthquake fault in the country. 

The USGS report warns that “hundreds of homes are built directly on its trace and mass transit corridors, major freeways and many roadways cross it in scores of locations.” 

According to a September 2007 U.S. Bureau of Labor Statistics report, more than 1.5 million Bay Area employees with a combined income of $100 billion working near the fault would experience strong tremors from a modern recurrence of the 1868 quake. 

“We are trying to get people to do the right thing,” Brocher said. “An earthquake of this size is larger than most cities can handle. Cities will require help from the state government who in turn will require help from the federal government. The more people can take care of themselves, the faster they can recover. Ninety-nine percent of us are going to be fine after the earthquake, but we need to have supplies and first aid training.” 

USGS is working on a scientific website which will illustrate the cause and effect of the 1868 earthquake drawing on scientific and historic information. 

With the help of software from Google Earth, viewers will be able to see modeled shaking of the earthquake, relocations of historic photographs, reconstruction of damaged buildings as 3D models and other scientific data.