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Reports Warn of Tsunami Danger

Waves hitting the West Coast could be as high as 100 feet after a quake, scientists say.

December 13, 2005|Sharon Bernstein | Times Staff Writer

A year after the catastrophic Indian Ocean tsunami, two new reports conclude that California is still a long way from protecting its residents from earthquake-generated waves.

While risk of a major tsunami is not as big as that of a large earthquake striking on land, seismic safety experts and seismologists said California has failed to adequately prepare for the rush of water that would follow a big ocean-based temblor.

Recent work by British and American scientists even raises questions about the most basic approach California officials are taking to tsunami preparation. Their research indicated that the waves generated by a massive underwater quake could be three times as high as previously believed -- potentially creating a much larger disaster than state officials have been planning for.

Scientists comparing the fault zone that caused the Indian Ocean tsunami -- which reached 60 to 80 feet in places -- with a similar region off the coast of the Pacific Northwest say that California, Oregon and Washington could be vulnerable to 100-foot waves.

By contrast, West Coast cities and states have been preparing for waves about 33 feet high, based on computer models of a breach along the Cascadia subduction zone, which runs nearly 700 miles along the coast and is capable of producing a magnitude 9.2 temblor.

But even those plans have huge gaps, according to a report released Monday by the California Seismic Safety Commission, with few realistic evacuation plans for coastal cities, inappropriate building codes for coastal zones and little understanding among the population about what to do in the event of a catastrophic rise in ocean level.

The findings are sober news and come after a major temblor off the Northern California coast last spring prompted a local tsunami alert. But some police and fire departments complained the state was slow in bringing them word about the alert, making it difficult to decid whether to issue evacuation orders. No damage was reported from that quake.

More than a million people in California live in areas that would be flooded by a tsunami, and another million visit the state's beaches on a typical summer day, according to the Seismic Safety Commission report. While the cliffs along much of the state's coastline -- including significant portions of the Southern California coast -- would keep many seaside homes and businesses out of the way of high waves, the ports of Los Angeles and Long Beach would be vulnerable, the report said.

"Tsunamis, generated either locally or from events elsewhere in the Pacific Basin, pose a significant threat to life and property in California," wrote the Seismic Safety Commission in its report.

High waves could knock out the ports of Los Angeles and Long Beach for as long as two months, costing about $60 billion. Water would pour over the docks and terminals, which were built just nine feet above the mean high seawater level, the report said.

There have been 80 tsunamis in California over the past 150 years, and geological records show previous swells reached heights of 60 feet or more.

A gigantic quake and tsunami on the Cascadia is a relatively rare event, happening about once every 500 years. The last one was about 300 years ago, and the next could happen "anywhere from tomorrow to 200 years from now," said seismologist Lucy Jones, a Seismic Safety Commission member. (By contrast, experts expect a significant quake along the San Andreas Fault within the next 30 years).

But subduction zones in Alaska, Chile, Japan and other places have frequently produced smaller tsunamis, and experts say even a five-foot wave can be deadly, creating massive undertows, ripping ships from their moorings and flooding low-lying areas.

Evacuations would be difficult, because most Californians have not been taught to recognize the signs of an impending tsunami, or what to do should one occur.

The indications are simple, said Jones, who is scientist-in-charge for the U.S. Geological Survey in Southern California: a long earthquake felt near the beach, after which the water recedes.

"You need to know that if you have a five-minute earthquake, there will be a tsunami," Jones said. "That's inevitable.... The really terror scenario is that it's a summer day and there's a million people on the beach."

Beachgoers who feel a quake and see the water recede should run several blocks inland, Jones said. They should stay away for at least 12 hours, because tsunamis are really a series of waves that can last for hours.

But evacuating crowded beaches can be complicated.

Beachgoers in coves at the base of cliffs would have to fight each other to get up ramps and rickety stairways to higher ground. People in low-lying areas would have to retreat far inland or find tall buildings to climb.

The state has hired scientists at USC to prepare maps showing areas that would be flooded in a tsunami. These maps are supposed to be used to develop evacuation plans for local communities.

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