POSTED 30 JULY 1998
How can we protect ourselves?
As a force of nature, tsunamis make even tornadoes seem puny. But there are two things to do in the way of self-protection: Sound the alarm, and get to high ground.
The Pacific Tsunami Warning Center was established in Hawaii in the wake of the deadly 1946 tsunami. The Hawaii center has now been supplemented by warning centers in Russia and Japan, and a regional network focusing on Alaska and the West Coast.
Since almost all tsunamis originate in earthquakes, the warning centers rely on data from seismographs across the unstable geology of the Pacific Ocean's ring of fire. It is here, where plates of the earth's crust are colliding, that many giant earthquakes originate.
All magnitude-7 earthquakes in the Pacific basin that are undersea or near the coastline will trigger a tsunami watch. Tsunami warnings go to locations within three hours travel of the first wave. (A watch indicates that a tsunami is possible. A warning indicates that one is highly likely or confirmed. Both alerts carry predicted arrival times for all areas in the path of the waves.)
Paul Whitmore, assistant director of the West Coast and Alaska Tsunami Warning Center, says the center can issue alarms within about 10 minutes of a quake.
The decision to issue a watch or warning is based solely on the magnitude of the quake. Even though extremely deep quakes shake the ocean floor less than shallow ones, and are less likely to trigger giant waves, there is simply no time to factor in anything but earthquake magnitude in the initial alarms. Eventually, the seismograph readings are compared to data from special gauges that can read the elusive signal of tsunamis.
George Curtis, an ocean scientist who's president of the Tsunami Society, says the Pacific warning center has not failed to forecast a strong tsunami in 50 years of operation. (The New Guinea tsunami started so close to the coast that no warning was possible -- we'll discuss minimum warning times later.) Yet the essential challenge remains, he says: to issue accurate alarms without issuing too many false alarms.
The warning systems seem to be working -- the last tsunami deaths in the United States were in 1975 -- with the exception of one person killed by a local tsunami caused by a landslide in Alaska, Whitmore says.
Still, warning systems may never be quick enough to alert those living near the center of the earthquake. "People nearest the epicenter are likely to be on their own," says Whitmore. "We try to drum in the fact that if you feel a strong earthquake, enough to make it hard to stand up, and it lasts more than 20 seconds, you should get at least 100 feet above sea level."
In Hawaii, which gets hit by tsunamis from all points of the compass, that general wisdom has been supplemented by the maps of safe zones printed in each island's telephone book. Tsunami experts are trying to improve computer models of tsunami behavior so they can better anticipate how the waves move and where they strike.
One important area is figuring out how the elusive waves actually work. According to Harry Yeh, a civil engineering professor at the University of Washington, tsunamis can defy the conventional view of how waves operate. For example, he says, one tsunami destroyed houses in a cove without damaging a house on an unprotected headland. "It's the exact opposite of what a storm wave would do," he points out.
Blue-sky tsunami detectors
As we've said, in the deep ocean, tsunamis are so insignificant that no ship has ever detected one. Specialized gauges can spot tsunamis, but scientists like Curtis say advanced technology could provide for better detection, and ultimately better, more reliable warnings:
Sensitive radar altimeters on satellites could see the subtle rises in the sea that mark a tsunami's passage across open ocean. Although such altimeters exist, they would need to be in the right place at the right time, which they seldom are.
GPS (global positioning satellite) sensors aboard ships and buoys could detect tsunamis if they used military-precision GPS instead of the less accurate signals available to the public.
Pressure detectors on the sea floor, already being tested, can detect the change in pressure of a tsunami. These devices would send data to a surface buoy via sound waves; then to a satellite for relay to a warning center.
Basic tsunami safety
As they work on better detection techniques, tsunami experts say that public education -- and action -- is the best way to reduce the death toll. Here are some basic safety rules.
- Be on guard for strong earthquakes, which can spark a tsunami. If you feel one at the beach, run inland.
- Heed the warnings, and stay tuned to emergency radio stations.
- Never go down to the beach to watch for tsunamis -- they move much faster than you can run. People die doing this.
- Most structures in the danger zone provide no protection. However, the upper stories of tall, multi-story, reinforced concrete hotels can provide refuge if there is no time to quickly move inland or to higher ground.
- A tsunami is a series of waves. Don't go near the beach until you hear the all-clear from emergency authorities.
Here are the rest of the tsunami safety rules from which we shamelessly borrowed.
We found a tidal wave of information on tsunamis.
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive