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PACIFIC SCIENCE, Vol. XXI, October 1967 
Since only a very few of the thousands of earthquakes which occur annually cause tsunamis, 
it was also necessary to include tide stations in the Warning System to detect the waves. The 
Coast Survey’s network of tide stations was expanded and a tsunami detector was developed 
which filtered out tidal and wind waves. Tsunami traveltime charts were prepared to provide a 
rapid and easy method of estimating tsunami arrival times at tide stations in the Warning System. 
The military services and Federal Aviation Agency initially provided communication facilities. As 
the Warning System expanded, facilities of the Department of Defense and foreign governmental 
agencies were utilized. 
The Warning System began operation in August, 1948. Initially it consisted of the C&GS seis- 
mological observatories at College and Sitka, Alaska; Tucson, Arizona; and Honolulu, Hawaiif 
and nine tide stations. Today the System has 17 participating seismic observatories and 30 tide 
stations (see map). 
In addition to the United States and Chile, the Tsunami Warning System now provides warnings 
to Tahiti, Japan, Taiwan, Fiji, Hong Kong, New Zealand, Western Samoa, Canada, and the 
Philippines. 
