Geologist discounts new fault assessment Geologist discounts new fault assessment (October 27, 2004)

By Sheldon Breiner

A letter recently mailed to most Portola Valley residents advocates that the Town Center remain where it is. The author, a professor emeritus of civil engineering at UC Davis, advocates rebuilding the existing structures to withstand the shear forces that could come in an earthquake. He cites the 1975 Degenkolb report as evidence that this can be done.

What is different now than it was in about 1980, when these then-interim town facilities were scheduled to be vacated, is manifold: building codes are vastly more stringent; the buildings, which are anything but attractive, are at the end of their design lifetimes and cannot practically be improved in their present form; town staff and community use demands have grown and need yet more space; and more.

Engineers and geotechnical experts have presented informal opinions concluding that the cost of such seismic reinforcement to the current buildings would be prohibitive. In addition, state, federal and local law prohibit use or modification of such public buildings as --or where -- they stand. For these latter reasons alone, it is not worth spending hundreds of thousands of dollars on a feasibility design when the town owns perfectly suitable space without an active fault trace, as shown by a $250,000 state approved geologic study, and without the likelihood of damage from liquefaction.

The professor, James A. Cheney, also asserts that the structures themselves and tree roots will cause the fault to veer around its well-established active trace and thus avoid damage to the building and harm to its occupants. Putting our faith in tree roots is akin to having the council declare the town to be an "Earthquake Free Zone."

Would these buildings remain standing while straddling a fault where the two sides, at a depth of 20 miles and over a distance of 20 miles, have already shifted almost 12 feet since the great 1906 earthquake -- twice as much as it moved in 1906?

It is inevitable that the rocks on the surface have to catch up with the rocks on which and next to which they sit and will do so for the entire, locked-up northern California section of the fault, in separate large earthquakes or one very large seismic event.

Moreover, we know from 1906 pictures at the Town Center site and from numerous trenches just south of the Town Center, where the shear will take place; we just don't know when. But it will happen.

Would you, if you were a council member, and could somehow flout the law, knowingly approve the design and reconstruction -- at enormous cost and liability -- of a building to service the town's needs for the next 50 years and do so right smack dab on what is arguably the most notorious fault in the world?

Do not let our faults ruin our lives, figuratively or literally.

Sheldon Breiner is chairman of Portola Valley's Geologic Safety Committee.

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