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Tuesday, July 18, 2006

Tsunami is not freaque wave

The Australian newspaper “The Age” carried the following news commentary today:

AN EARTHQUAKE measuring 7.2 magnitude struck roughly halfway between Java and Christmas Island on Monday. The 300 residents of Christmas Island received a 20-minute warning of an impending tsunami. The residents of Java's seaside villages received none. At least 300 Indonesians died in the freak waves that swamped Pangandaran beach near the town of Ciamis. More than 400 were injured. Buildings have been washed away. Australians living in the region escaped by racing up a nearby hill to safety.

There is one thing distinctively striking in this news item from my vintage point: as the subject is all about tsunami, but it said “300 Indonesians died in the freak waves. This is a continuous confusion persisting out there in the media and general public – treating tsunami as synonymous with freaque waves. In fact they are really two distinctively different phenomena. Tsunami is a shallow water wave with very long wave length and wave period, it is harmless while traveling through the deep ocean at a constant speed equal to the square root of the product of the acceleration of gravity and the water depth. Only when its wave-crests reach shallow water region then all of their energy swiftly squeezed into much smaller spaces and cause huge walls of water to rise up, rushing along at speeds often too fast to apprehend. The resulted terrible destructive forces of tsunami are all too familiar. But its arrival time to some extent can be considered as predictable, although the prediction may not always be accurate. Freaque waves, on the other hand, are deep water waves with relatively shorter wave length and wave period, and it simply surged up into an unexpected high crest or deep trough out of the blue. Its destruction is sudden, instantaneous, and transient. We don’t know how or why it happens, we don’t know when it happens, and we don’t know where it happens. It is totally unpredictable at the present. Because of the long standing, continual confusions of calling tsunami as freak waves, it would be advantageous using our new term “freaque” waves for what it really is and averting any advertent or inadvertent confusions.

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