Newsletter article; Tsunami and Science
Tsunami and Science
How the application of science saves lives when tsunamis occur
by George Curtis
The tsunami warning system was developed in 1947-48 by scientists of the
U.S. Coast and Geodetic Survey and others. Since most tsunamis result from earthquakes
near or under the ocean, the scientists combined seismographs, oceanography, tide gauges,
observers, and communications into a system which has detected every Pacific-wide tsunami
since 1948. When an earthquake occurs, seismic waves travel through the earth, and are
measured and the quake located by instruments at the Pacific Tsunami Warning Center at Ewa
Beach, Oahu, and other locations.
A tsunami is a series of waves 10 to 20 minutes apart generated by the
heave and dip of the sea floor. As soon as the earthquake happens, tsunami waves begin to
spread out at the speed of a jet liner, but are already being analyzed and queries sent to
tide stations near the disturbance. (Some sea level gauges are telemetered to Honolulu and
can be read directly at the Warning Center.) If the earthquake magnitude is greater than
7, a "watch" (a caution, not a warning) is issued while waiting for more data;
but if the magnitude exceeds 7.5, a warning is immediately issued for shores within three
hours travel time of the first wave. Since the speed of the tsunami waves can be easily
calculated by knowing the depth of the ocean path they are crossing, the scientists at the
Center can check the observing stations at the estimated time of arrival of the first
waves. The reports and data from the gauges are evaluated with consideration for the
earthquake's magnitude and depth, the history of tsunamis from that area, and the
proximity to settled coastlines. In a few minutes, the scientists in charge must make a
difficult decision involving many human lives and millions of dollars, and it must be a
"YES/NO" decision. If they expect waves over 1 meter (3') high to impact an
inhabited coast, they will advise the civil authorities in that area; it is up to them to
handle the evacuation of "low-lying areas". Because the waves travel about 500
miles an hour, they then advance the warning across the ocean to stay three or four hours
ahead of the first wave, while evaluating the impact on the areas already affected to
verify if the warning must be continued and expanded.
The Pacific Tsunami Warning Center is operated by the U.S. and involves 26
countries which may send gauge data and receive the watch and warning messages. A local
system is maintained in Alaska and issues warnings on seismic data alone for events near
Alaska; there is not enough time to verify the waves as evacuation must be almost
immediate. The Center at Ewa Beach provides the same service for local events in Hawaii.
The Japanese maintain a center for events in their part of the ocean, as do the Russians,
with the evaluation method dependent on the time available.
There are a few important things for Hawaii residents and visitors to
remember when there is a tsunami warning: if you hear Civil Defense sirens or see a TV
message about a possible tsunami, turn on a radio and follow instructions. Don't use the
telephone! Instead, check the maps in the front of the phone book to see if you are in an
evacuation zone. If you are at the beach and feel the ground shake hard, you just received
nature's warning of a local tsunami. Run for high ground without waiting for sirens! If
you want to read more about this application of science, see:
Zetler, Bernard. 1988. Some Tsunami Memories. Science of Tsunami
Hazards, Vol. 6, No. 1.
Curtis, George. 1993. The Tsunami Research Problem. Science of
Tsunami Hazards, Vol. 11, No. 2.
Dudley, Walter and Min Lee. 1988. Tsunami!. University of Hawaii Press..
These and many other publications can be found at the University of Hawaii
George Curtis is a tsunami research specialist with the Joint
Institute for Marine and Atmospheric Research at UH- Manoa. He lectures in Marine Science
& Physics at UH- Hilo and is a member of the museum's Scientific Advisory Council.
George developed the tsunami evacuation maps Civil Defense has placed in all Hawaii
Telephone Directories and is the Hawaii County Tsunami Advisor.
All materials © Copyright 1996-2007 Pacific Tsunami Museum Inc.
130 Kamehameha Ave Hilo, HI 96720 tel: 808-935-0926 FAX: 808-935-0842
Last Revised November 2007