California Geological Survey Announces New Hazard Maps

New tsunami hazard maps highlight threat facing seven California counties — even Napa is at risk

By The Chronicle’s Editorial Board —

Published: May 28, 2013

For the first time, there are new hazard maps issued by the California Geological Survey, warning about threats to seven California counties because of the magnitude and possible duration of a coming Pacific-wide typhoon.

The new maps, available on the Web at, show the threat on county and beach elevations. In many cases, the maps show that beaches may be washed out for a few days, possibly for several weeks.

In general, the threat to beach-front communities is the same. In all seven cases, the threat is from flooding or debris, and there is a possibility of tsunami.

However, the maps differ from earlier maps put out in the spring by the agency. In earlier maps, all the beaches in one county were at a similar risk and the threat to all of San Francisco Bay was considered.

In the six-county region, the hazard maps show that three of the seven beaches would be washed out for all or part of two to three days, and some for several weeks.

On the other hand, there was no tsunami threat, which is important for residents who live on or near a tsunami-active coast.

Many of the most vulnerable beaches have the same elevation. The risk to beaches on the Pacific and Atlantic coasts is the same, but the hazard is higher because there is a wider range of elevation on the Pacific side.

On most of the beaches, the hazard is less severe than on the San Francisco Bay coast. But, as in the Bay, there also is a possibility of a tsunami.

On beaches where there is the same elevation, the highest hazard lies in Monterey County, where the hazard is highest, followed by Santa Cruz County, which is next in line.

On the other hand, the hazard is the greatest on the coast south of San Jose. And it is the least on the coast to the north of San Francisco.

The new hazard maps are prepared with greater accuracy because the new threat

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