published Friday, March 11th, 2011

California coast not as vulnerable as Japan's but still susceptible to tsunami damage

  • photo
    A boat sinks into the ocean in the aftermath of the surge caused by a tsunami on the harbor in Santa Cruz, Calif., Friday, March 11, 2011. A ferocious tsunami unleashed by Japan's biggest recorded earthquake slammed into its eastern coast Friday, killing hundreds of people as it carried away ships, cars and homes, and triggered widespread fires that burned out of control. Hours later, the waves washed ashore on Hawaii and the U.S. West coast, where evacuations were ordered from California to Washington but little damage was reported. The entire Pacific had been put on alert _ including coastal areas of South America, Canada and Alaska _ but waves were not as bad as expected. (AP Photo/Marcio Jose Sanchez)

By Matt Weiser

SACRAMENTO, Calif. — Much of California is less vulnerable to the kind of tsunami wreckage caused Friday in Japan because the state's coastline is generally steeper, a University of California quake expert said.

Steven Ward, a research geophysicist at UC Santa Cruz, said there are exceptions to that statement, including the Los Angeles coastal plain, many harbor areas, and any place where a major river enters the sea, such as the Moss Landing area at Monterey Bay.

But in general, he said California's steep bluff-encrusted shore would block the kind of broad waves that swept buildings and ships far inland in Sendai, the Japanese city of 1 million people near the epicenter of Friday's quake.

Ironically, he said it is the San Andreas earthquake fault that keeps California's coast so steep.

"Even big waves typically can't go very far inland because you have bluffs and whatnot," said Ward. "So the actual inundation zones are fairly limited. We're lucky that way."

Even so, the 8.9-magnitude quake, which struck at 9:46 p.m. Pacific time Thursday, has caused damage in several California coastal communities as tsunami waves swept ashore Friday.

Crescent City experienced an 8.1-foot wave swell from the tsunami Friday morning, the largest reported so far in California. Officials evacuated about 6,000 people hours before that wave. The Associated Press reported one dead and three people missing, with lots of damage to boats and marina infrastructure.

The U.S. Coast Guard is currently searching for a man who was swept out to sea near the Klamath River in Del Norte County after he and a friend went to the coast to take pictures of incoming tsunami waves.

Six boats were also sunk in Santa Cruz and a harbor there was damaged as people flocked to watch.

Ward said traveling to the coast to watch the waves roll in is not a good idea, because tsunami waves can be very unpredictable in terms of their size and timing. They have a much longer "period," or time between crests, than the routine waves people are accustomed to seeing. Hours might separate tsunami waves, and the first one is not always the biggest.

The waves also tend to travel at 30 miles per hour across land, which is too fast to run from.

U.S. Geological Survey officials said Friday that the quake was about 30 times more powerful than the 1906 San Francisco quake. It caused a 50-foot uplift in a section of sea floor off the coast of Japan stretching 180 miles long. This caused a huge "bulge" of sea water big enough to spread all the way across the Pacific, which is the source of the tsunami waves.

"It's probably among the top five (earthquakes) that's ever happened in history," Ward said. "The ocean is nice when it's quiet, but it can be a fiend when it kicks up."

The State Parks Department evacuated and closed dozens of Northern California beaches and coastal campgrounds under its jurisdiction Friday morning as a precaution. They will remain closed as long as the tsunami warning is in effect.

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