U.S., States Seek to Flood West Coast With Tsunami Warnings
The next time you visit a Pacific Ocean beach, you may find a new addition to the signs that warn of dangerous undertows and riptides.
The blue-and-white signs show a person running from a giant wave. The message: “Tsunami hazard zone. In case of earthquake, go to high ground or inland.”
Tsunami is the Japanese name for renegade sea waves up to 100 feet high that are generated by earthquakes or landslides.
And the person on the sign is probably out of luck trying to outrun the wave looming behind him. Although the waves don’t maintain their 500 mph top speed on shore, the pace of 30 mph to 50 mph is faster than humans can run.
That’s why the federal government and the states of California, Oregon, Washington, Alaska and Hawaii want to improve the technology used to detect tsunamis and increase civil-disaster planning and public education.
“We know that we’re due for a big one,” said George Crawford, earthquake program coordinator for Washington state’s emergency management division.
The threat is not new.
Most of the 132 people killed in Alaska’s 1964 Good Friday earthquake were victims of tsunamis. About 20 of the estimated 121 tsunami victims were outside Alaska as the waves ravaged other parts of the West Coast.
In Hawaii, tsunamis are the deadliest natural threat, blamed for more than 300 deaths since the 1940s.
Over the last century, there has been an average of one damaging tsunami per year in the Pacific basin, with a 100-year toll of about 70,000 people. In just three years, from 1992-1994, half a dozen tsunamis over 15 feet tall killed more than 2,300 people.
But the threat has taken on new urgency with evidence in the last 15 years that a coastal earthquake zone from Northern California to British Columbia--the Cascadia subduction zone, where plates of the Earth’s crust are colliding--is capable of generating giant quakes that could send tsunamis crashing ashore in a matter of minutes.
It really hit home in April 1992, when a 7.2-magnitude quake struck off the coast of California’s Humboldt County.
“It created a massive amount of damage in Northern California . . . and it produced a small tsunami” about one to three feet high, said Eddie Bernard, director of the Pacific Marine Environmental Laboratory here and chairman of the National Tsunami Hazard Mitigation Program.
“Now, this was the first time that California had had a subduction-zone earthquake and an accompanying tsunami,” Bernard said. “That woke up everybody.”
Before that, officials had believed that there would be hours of lead time for a tsunami threat.
“Humboldt really turned all of that on its head,” said Richard Eisner, the regional administrator for the coastal region of California’s emergency-services agency.
The U.S. Senate asked the National Oceanic and Atmospheric Administration to assess the threat and state preparedness. But as Bernard began organizing meetings, he found that the federal officials responsible for issuing tsunami warnings, and the local officials responsible for dealing with the results, didn’t know much about each other.
A steering group of representatives from federal agencies and the five states came up with a three-pronged approach:
* Hazard assessment. A center was set up last year in Newport, Ore., to help produce “tsunami inundation maps,” showing coastal areas that would be flooded by tsunamis. Local officials can use the maps to plot evacuation routes or decide locations for critical facilities such as fire stations and hospitals.
* Warning guidance. The region’s network of seismic stations is being expanded and upgraded to better track the source and type of earthquakes for NOAA’s tsunami warning centers at Ewa Beach, Hawaii, and Palmer, Alaska. A series of at-sea buoys that detect water-pressure changes also is planned, to detect tsunamis and determine their size. And research and warning centers are integrating their computer systems, so each can have access to data from the others’ arrays of seismometers.
* Mitigation. The “tsunami hazard zone” signs are one example, along with signs marking evacuation routes, informational brochures, school-evacuation drills, warning systems such as sirens, and other local efforts.
The “inundation maps” offer insights, but aren’t intended to dictate land-use planning.
“What you can say is that, in general, if an earthquake occurs like we envision and if a tsunami is produced like we envision, then this area will probably be flooded,” Bernard said.
“If your house is in the middle of it, that doesn’t necessarily mean you’re going to get blown away, but I would recommend that you figure out a way to protect your family in the event this happens.”
Congress appropriated $2.3 million for the joint effort this fiscal year and the same amount last year, with the states contributing as well.
“Our problem is like everybody else: It’s resources,” said Jim Mackin, mitigation officer for the Alaska’s emergency-services division.
“When they’re made available and there’s not a lot of strings on it, it’s great,” he said. “What we need to do in Alaska is different from what they need to do in Oregon and California.”
From NOAA’s standpoint, a major goal of the program is to eliminate false alarms that cause unnecessary evacuations, such as one in October 1994, when a magnitude 8.1 earthquake off Russia’s Kuril Islands spawned a tsunami. The wave turned out to be a wash in U.S. territory--but not before disrupting life in numerous West Coast communities.
Warnings issued by NOAA’s tsunami warning centers now are based strictly on the size and location of an earthquake--an ultraconservative approach for safety. It’s not known whether a tsunami has actually been generated until the wave reaches one of a series of tide gauges around the Pacific.
If the tsunami is small or nonexistent, the warning is quickly called off. The planned deep-sea buoys--half a dozen of them from Alaska to Chile--should be able to tell quickly whether--and how big--a tsunami has formed.
False alarms are pricey: Hawaii has calculated the cost of a statewide evacuation at $40 million per day, mostly due to lost business, said Barbara Hendrie, a spokeswoman for Hawaii State Civil Defense.
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Some facts about tsunamis, the big sea waves most frequently generated by earthquakes:
The word: Tsunami is a Japanese word that translates as “harbor wave.” The term “tidal wave” is inaccurate, since tides have nothing to do with their formation. The term “seismic sea wave” is also misleading, since tsunamis can also be generated by such non-seismic events as landslides and meteorites. Such tsunamis generally dissipate more quickly than those that follow earthquakes.
What it is: Unlike wind-caused waves, which are fairly short and only a few seconds apart, a tsunami may stretch dozens of miles in length, and the time between one tsunami and the next can be an hour or so. In the deep ocean, where they move fastest, they can travel at speeds up to 500 mph.
Earthquakes and tsunamis: An earthquake can generate a tsunami if the quake involves a sudden rising or lowering of part of the sea floor. That abrupt change displaces the water above, and a tsunami can form as the water moves to regain its normal surface.
How tsunamis look: In the deep ocean, a tsunami is imperceptible to humans. As a tsunami reaches shallower depths near shore, its height can rise several yards or more. When it reaches shore, it may appear as a rapidly changing tide, a series of breaking waves, or a bore--a high, abrupt wave in a narrow channel.
On shore: Tsunamis can inundate areas hundreds of yards past the normal high-water mark, stripping out soil and crushing structures. They can reach heights of 100 feet.
Sources: University of Washington Geophysics Center; National Oceanic and Atmospheric Administration