Palo Alto Weekly

Cover Story - February 25, 2011

Living on the fault line

State laws require disclosure of natural hazards to potential home buyers

As the curvy Highway 84 in Woodside winds its way west toward the coast, the road makes an elbow-like turn to the south, running through the San Andreas fault zone.

At the bend, a stone pillar marks a road running straight into the heart of the fault: Why Worry Lane. The words are carved deep into its fašade.

The neat road leads into a neighborhood of several homes, situated between three branches of the fault, according to a state map. Just to the north, Tripp Road parallels the fault. The fault creeps slowly here, about 17 millimeters a year, according to geologists. Sometimes the earth quivers like jelly; at other times it bounces and jolts — or rocks and undulates.

Karl Olson is not concerned. His parents knew about the fault when they purchased the home on Tripp 40 years ago, he said.

"People kind of know what they're getting into," he said.

Several state laws govern the information that sellers must disclose about natural hazards to potential home buyers.

Under the Alquist-Priolo Act, state-generated maps indicate where active faults are located. The law was passed in 1972, following the destructive Feb. 9, 1971, magnitude 6.6 San Fernando earthquake, which damaged numerous homes, commercial buildings and other structures after the earth's surface ruptured.

The maps are distributed to cities and state agencies to aid in regulating new construction or remodeling within the zones, according to the state Department of Conservation.

But single-family wood-frame and steel-frame homes of up to two stories that are not part of a development of four units or more are exempt from Alquist-Priolo.

Cities and counties must require a geologic investigation to be sure that proposed buildings are not constructed on active faults. If an active fault is found, the building must be set back by at least 50 feet.

A later law, the 1990 Seismic Hazards Mapping Act, addresses other kinds of hazards, such as liquefaction and earthquake-triggered landslides.

Palo Alto Realtor Lydia Kou said the 1998 Natural Hazards Disclosure Act addresses homes in seismic-hazard zones. A remodel might have restrictions if the home is in a fault zone, which can be an issue for homeowners who want to convert a smaller home into a much larger one, she said.

Kou researches earthquake zones on maps such as Barclays Locaide, which combines natural-hazard zones with other boundary information, such as city districts, schools and town boundaries. But she also reviews hazard maps at city planning departments, where finer details and smaller "tributaries" or fault branches are shown, she said.

Earthquake fault-zone maps can be viewed at local planning departments or through the California Geological Survey. The maps show streets, drainages and other features in relation to the fault zone. Some cities add fault-zone boundaries to parcel maps, according to the conservation department.

Olson found a surprise one day while viewing a Woodside town map, he said.

"Apparently (the fault) cuts right through our corral, which I found sort of interesting."

— Sue Dremann and Sarah Trauben

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