CALCULATING CALIFORNIA'S TSUNAMI RISK

The threat that Pacific Ocean tsunamis pose to California's coastline just got its first comprehensive study, a milestone in understanding and preparing for the rare, but devastating, waves.

Following the devastating 2004 tsunami in southeast Asia, scientists scrambled to provide county and municipal emergency planners with an estimate of how vulnerable their coastlines were to tsunamis.

Some 350,000 people live in the path of a worst-case scenario, though overall, the risk to life and property is less than previously thought, state officials reported.

"We used one elevation for the whole state. We just drew a line at 30 feet up from sea level," Rick Wilson of the California Geological Survey said.

With the new effort, Wilson and a team of researchers developed detailed maps of what parts of the coast would flood during a range of disaster scenarios.

Overall they found that most surges wouldn't come close to the 30-foot line they had previously assumed.

"Even if we don't show higher inundation, this really helps emergency planners," Wilson said.

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This is particularly true on the outskirts of San Diego, where the city of Coronado sits on a low-lying peninsula. Old tsunami maps predicted the entire town would be submerged, and local officials feared that they would be forced into a desperate attempt to airlift 24,000 people out of harm's way.

New maps predict the worst waves would reach elevations of 15 to 18 feet.

Large earthquakes can generate tsunamis just about anywhere along the Pacific "Ring of Fire," a 40,000-kilometer-long chain of tectonic unrest that includes Japan, Kamchatka, the Alaska's Aleutian Islands, the Andes in South America and California.

The team considered threats from all of these regions, and found that a magnitude 9.0 or greater earthquake in the eastern Aleutians would be the most dangerous for California.

In particular, Santa Cruz could see waves of 20 to 25 feet. Even the interior of the San Francisco Bay would not be spared, with 10-12 foot waves reaching Alameda, and eight- to 10-foot surges spilling into the towns of Sausalito and San Rafael.

"Any emergency responder can look at these maps and see what it means for them and their neighbors." Dale Cox of the United States Geological Survey in Sacramento said. "It's intellectually accessible to the public, too. If people are asking 'gee, where do I go?' these maps will tell you. People can look at these and easily tell what's in it for them."

Source: Discovery News