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Name: Robert
Status: Other
Age: N/A
Location: Arkansas
Country: United States
Date: January 1, 2005


Question:
I was amazed to find out that the Maldives were not completely destroyed by the Banda Aceh Tsunami even though they are in a direct line with the focal point between Somalia and Sri Lanka. Did the seabed topography cause this surprising result?



Replies:
Like thousands of others the recent tragic events sent me on searches to find out what I could about tsunami. There is a lot of literature on the Web and no doubt much more in print. What I found surprising is that tsunami dynamics are not well understood. Only a fraction of earthquakes, even those with epicenters in the ocean produce tsunami. Volcanic action can also cause tsunami (the most famous being the volcano Krakatoa in the same general region in the latter part of the 1800's). The wavelength of the waves is very long and the speed of the waves is very fast in deep water. Just how the wave "breaks" -- I think the technical term is "shoaling" depends a lot on the local topography as the water becomes shallow. These phenomena are difficult to study because they are fairly rare, they affect a significant fraction of the globe and being so destructive are likely to destroy monitoring equipment. In addition, unless there is some sort of global "early warning network" they strike with so little warning that it is too late when one recognizes that something horrific is about to happen. In addition, the most seismically active areas of the earth are in that area of the globe where rapid communication is very difficult.

Vince Calder



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