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[whitespace] Faulty Towers

Evergreen Valley--Most experts agree that the folks who buy one of the houses sprouting up in East San Jose's newest residential community won't have to worry about their houses collapsing in flame and rubble.

But nobody can absolutely promise that it won't happen.

The Evergreen Fault--a thrust fault similar to the one that munched Northridge in 1994--runs smack dab under the land where a dozen homes and a 54-unit condominium complex are under construction.

Mike Shimamoto, San Jose City Geologist, isn't worried.

"We've tried looking for that fault," he says. "If you go out to the area where it's supposed to be, there is virtually no evidence that there is anything there."

Several faultlines meander along the base of the East San Jose hills where a total of 2,996 new housing units are new being built. Both branches of the Evergreen, as well as the Silver Creek and the Quimby Faults--believed to have helped form the eastern slope of the Santa Clara Valley--skirt the development. The mighty Hayward and Calaveras faults lie just to the northeast.

City Geologic Hazard Maps show the Evergreen Fault as slicing straight through the western end of the Evergreen Specific Plan. Yet construction in the fault's path was approved in back in 1991, after Shimamoto accepted a consultant's report which concluded that "neither the Evergreen nor the East Evergreen Faults have been mapped on this site."

Just a mile south, after digging for evidence of seismic activity in 1994, Evergreen Valley College decided to move the planned site of a new student center clear of the Evergreen Fault.

"We trenched the fault, and we do think we found it," says Ivan Wong of Woodward-Clyde Consultants. "We don't think it's moved for 11,000 years or possibly much longer. It hasn't broken the surface, but that doesn't mean it can't generate an earthquake. Northridge never broke the surface."

The Evergreen Fault was also spotted at a site three miles northwest of the Evergreen Specific Plan. The fault was interpolated between those sites on Santa Clara County Seismic maps and Barclay real estate maps as running straight through the west end of the development.

Usually, in cases where the position of a fault is known, construction can proceed safely with the structures set back a prescribed distance from the fault. No such setbacks were recommended in the Evergreen Specific Plan.

"If you can find a fault and see it, it's a good idea to set back from it," Shimamoto says.

But in this case, he argues, "there is nothing to set back from."

In searching for the exact location of the fault, city consultants excavated seven trenches, ranging from 10 to 15 feet deep. They came up with nothing. If the fault does exist on that site, it lies deep beneath ancient alluvial deposits and does not come up to the ground surface.

Experts believe the Hayward Fault poses a bigger threat to the new housing development than its local cousin. Incredibly, there are plenty of structures straddling that far more dangerous fault all the way up the East Bay.

"If you want to find out where all the hospitals and fire stations are [in the East Bay] just go over the Hayward Fault," jokes Wong.

The historic Mirassou Winery, also within the boundaries of the Evergreen Specific Plan, has been hit by temblors over the years that shook its huge wine barrels. But that shaking likely came from the Calaveras Fault, says Deborah Hardin, geology professor at San Jose State.

As the valley builds out, more and more people are going to live on or near the faultlines. If not an imminent danger, they serve as a constant reminder that the cities by the Bay are built on shaky ground.
Michael Learmonth

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Web extra to the August 27-September 2, 1998 issue of Metro.

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