Bay Area Fault Poses Major Threat, Experts Say

Scientists and engineers said Thursday that a magnitude 7 earthquake on the northern segment of the Hayward fault--running through the most heavily populated areas of the East Bay--would be nearly twice as damaging as the 6.7 Northridge quake.

In pegging possible losses at $32 billion and casualties at 20,000 dead and injured, speakers at the annual meeting of the Earthquake Engineering Research Institute explained that the most affected cities--Richmond, Berkeley, Oakland and San Leandro--have many more old buildings built before code revisions than Northridge and surrounding communities.

They added that liquefaction problems--where weak soils turn to jelly in heavy shaking--extend over far more land in the Bay Area than was the case in the Northridge quake and that serious damage would occur in San Francisco across the bay.

Statistically, this part of the Hayward fault is due for a major quake. The last big earthquake on the segment occurred in 1836, and scientists have calculated the recurrence interval at 167 years, plus or minus 67 years.

This means that the 30-mile-long segment “is close to or at failure” and that a quake could occur at any time, although it could happen as late as 2070, said David P. Schwartz of the U.S. Geological Survey. If the quake were to occur at the average interval, it would happen in 2003.

A northern Hayward fault quake could cause settling in the Sacramento-San Joaquin delta, which would allow an intrusion of saline waters from the bay and shut off freshwater supplies through the California Aqueduct to Southern California for months, said William R. Lettis, a liquefaction specialist from Oakland.

Lettis also warned of possibly hundreds of landslides in the Berkeley and Oakland hills, causing extensive damage to homes.

There is a chance, Schwartz said, that a big quake could extend into the southern segment of the fault running past San Jose, which last ruptured in 1868, or northward into the related Rogers Creek fault in Solano County.

Hundreds of geologists, engineers and government officials charged with preparing earthquake mitigation plans are attending the three-day meeting.

The huge San Andreas fault passes just off the San Francisco coast, but scientists have long contended that a Hayward fault quake could cause more damage and casualties in the Bay Area because it passes directly through populated areas.

Structural engineer William Holmes, vice president of the firm Rutherford & Chekene, said that the fault passes by the UC Berkeley football stadium and that the stadium’s construction is similar to that of the Los Angeles Memorial Coliseum. The Coliseum sustained $95 million in damage from the Northridge quake 30 miles away.

Holmes also estimated that a Hayward fault quake would lead to a shortage of hospital beds in the East Bay counties of Contra Costa and Alameda.

He said that of 3,530 such beds now available in Alameda County, only 984 would be left fully operational, while 1,338 others would be of limited service and 1,208 would not be usable at all. Of Contra Costa’s 1,748 beds, he estimated, 847 would be operational, 586 of limited service and 315 not usable.

This means that many of the injured would have to be transported across the bay or inland to Stockton or Sacramento, he said.

Brian H. Maroney, a senior bridge engineer for the state Department of Transportation, said he believes that the San Francisco-Oakland Bay Bridge--which lost a short span in the 1989 Loma Prieta earthquake--would survive a northern Hayward quake intact if retrofitted before it happens.

Retrofitting for the bridge is now in the design stage, Maroney said.

But he said the main East Bay freeways might suffer a series of collapses or disruptions similar to those of major freeways during the Northridge quake.

John Egan of Geomatrix Consultants said that a quake on the Hayward fault could disrupt the Bay Area Rapid Transit system, which had remained in service after the Loma Prieta quake. He cited a tunnel closure on the line to Walnut Creek and Concord and liquefaction damage on the main line to San Francisco near the West Oakland station as possibilities.