Concerned Tsunami Experts
Busy Studying West
Coast And Hawaii
By Keay Davidson
San Francisco Examiner
Scripps-McClatchy Western Service.
SAN FRANCISCO -- Last week's catastrophic tsunami in Papua New Guinea could be repeated anywhere along the West Coast of the United States, experts say.
Indeed, it's only been 34 years since a far more moderate tsunami struck the California coast, killing11 people in Crescent City.
To prepare for such a disaster, state and federal officials and scientists in California, Oregon, Washington, Alaska and Hawaii are busy:
Establishing a deep-ocean array of seismographs that can, via satellite, transmit warnings of tsunamis to the West Coast -- perhaps up to hours in advance --giving people time to flee to higher ground.
Trying to identify West Coast harbors, coastal towns and bays most vulnerable to tsunamis.
Trying to increase awareness of the tsunami risk to the West Coast.
The Papua New Guinea tragedy, which killed at least 1,300 and as many as 6,000 people, "might be a wakeup call for people living near the ocean in earthquake-prone areas," says oceanographer and tsunami expert Eddie Bernard of Seattle. "I'm not saying this as an alarmist, I'm saying it as a point of fact: This is a hazard you need to be concerned about, just as you need to be concerned about other hazards in your everyday life."
By 2001, scientists from the National Oceanographic and Atmospheric Administration expect to finish installing six tsunami-detecting buoys in deep Pacific waters, says Bernard, who chairs the National Tsunami Hazard Mitigation Program run by NOAA.
Two buoys are being tested just off quake-prone Alaska. They are attached to seismometers on the ocean floor that sense major oceanic quakes.
A wire transmits the quake signal to the buoy on the water's surface. From an antenna on the buoy, the signal flies via satellite to the nation's tsunami-warning centers near Palmer, Alaska, and Ewa Beach near Honolulu.
Much of the tsunami-awareness program stems from 1992, when a 7.1-magnitude quake in the Cape Mendocino-Petrolia area caused a relatively harmless tsunami, perhaps up to 3 feet high, on the north coast. By the time the tsunami hit Point Reyes, it was only 5 inches high.
But to the shock of scientists, the wave persisted up to eight hours as it bounced up and down the coast, "like coffee sloshing in a coffee cup," as Bernard puts it. I twas an ominous hint that researchers might have underestimated a future super-tsunami's duration and potential punch.
How bad would a California tsunami be? Certainly not as bad as the skyscraper-swallowing wave -- triggered by a falling comet -- in this summer's blockbuster, "Deep Impact."
But a California tsunami could be pretty bad, nonetheless.
The 15- to 20-foot-high tsunami in Crescent City in 1964, triggered by a huge Alaska earthquake, killed11 and wrecked 30 city blocks.
"In 1812 in the Santa Barbara Channel, there was a tsunami more than 8 feet high that hit fur-trading ships," Bernard said. "One was swept inland a quarter of a mile."
In 1994, Professor Kenji Satake of the University of Michigan ran a computer simulation indicating that a magnitude-9 quake off the California-Oregon coast could send a 6-foot wave crashing into Fort Point by the Golden Gate Bridge.
Catherine Firpo, emergency services coordinator at the state Office of Emergency Services in Oakland, says the state's tsunami mitigation effort is worth it: "Given the proximity of California populations to coastal areas, it's not unreasonable to prepare to respond to a coastal disaster such as this."
The California mapping program is led by USC civil engineering Professor Costas E. Synolakis, who couldn't be reached for comment. He has long warned that Californians might have under-rated the tsunami risk.
In 1994, Synolakis suggested that offshore thrust faults, which move vertically rather than horizontally, could trigger a particularly severe tsunami. In a worst-case scenario, he and a colleague said, a bizarre type of tsunami called a dipole wave -- generated just off the Southern California coast -- might wreak even worse damage than long-distance tsunamis.
Since NOAA is identifying the most vulnerable West Coast sites, the scientists' first concern is towns and cities directly on the coast, right in the face of an incoming wave.
"We (at NOAA) haven't done the study for San Francisco yet -- but that's on our list," Bernard said.
He said that in all likelihood a major tsunami entering the Bay "wouldn't propagate with a lot of speed -- but it would let a lot of water in," flooding low-lying areas in the Bay Area.
The San Andreas Fault runs out to sea just south of San Francisco .It is a kind of fault, known as strike-slip, that is less likely to cause a tsunami, because it moves horizontally rather than vertically. By contrast, major vertical faults exist off Los Angeles and the Pacific Northwest.
Tsunami concerns also have risen because of growing evidence that Pacific Northwest coastal quakes could be far worse than previously imagined. Pacific Northwest mega-quakes occur every several centuries, geological clues suggest.

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