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Postby juhuliane » 25 Feb 2013, 09:12

How long before tsunami after earthquake happens? An earthquake struck in Japan and a tsunami is expected. What is the length of time between the earthquake and the tsunami?
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Last edited by juhuliane on 27 Feb 2013, 08:30, edited 1 time in total.
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Re: tsunami

Postby Matte » 26 Feb 2013, 11:37

Depends on how far the earthquake epicenter is from the shoreline.

From what have seen (I am not a oceanologist) a tsunami will travel very fast in open water over the deep sea (from 700 to 900 km/h), but it would not be a big wave and I doubt you would even notice it passing even in a small boat. But it will be slowed down significantly as it reaches shallow water (basic newtonian physics) as it will increase in height.

If the tsunami forming earthquake epicenter is 300 km form the shore you have at least 20 minutes to get to higher ground if you are near the shore. Depending on the seabed topography near the shoreline you will get more time as the wave is retarded by the shallows. The basics for estimating this can be found in newtonian physics just apply conservation of momentum and you will get an idea of how much the wave is slowed down. I am sure one of our physicist can fill you in with the details if required...
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