PerennialII said:

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Wonder how fast can those things travel ... isn't there like a possibility to give a warning or something after the quake is registered, the word tsunami alert rings some bells ? Was just wondering since it did happen quite far off from India and Sri Lanka, which appear to have suffered the most.
Considering the depth of the sea in the are, i'd say around 700/900 Km/h
The deeper the sea, the higher the velocity.
A tsunami only becomes destructive once the seafloor starts rising.
Then the water column and velocity (due to friction with the rising seafloor) decrease.
The energy "stored" in the 6Km column of water can't just disapear.
In other words, it has to go somewhere, in case of a tsunami it means the watercolumn elevates abouve the normal sealevel.
By how much is dependable on how steeply the seafloor rises and the original depth and velocity.
In Sri Lanka the sea floor rises very steeply from around 5Km deep to the surface, in other words the actual wave hitting the beach is enormous.
From the coastline land inwards, the land is rather flat, in some parts even diving below the normal sealevel.
Because of this the wave can penetrate the land for a great distance before it has lost enough of it energy to no longer be destructive.
I believe in Sri Lanka the wave penetrated the land for over a Km before finally loosing its power.
After the wave has lost its power, the water will start running back to sea, the current will drag anything that is loose or not bolted (very securely) back into the sea.
Ant human trapped in this current (and miracilously is still alive) will most likely be crushed to death by debry.
In short, a Tsunami is a *****.
About the warning part.
In Thailand the communications are good enough to be able to warn a lot of ppl with an 45min warning.
This is not the case for small islands and most of India/Shri Lanka, this is the reason most of those ppl didn't know what hit them.
Ironically, a lot of ppl actually came to the shore to whatch a mysterious drop in sealevel, a prelude to a Tsunami.
To bad they didn't know what the were looking at.