[LINK] Tsunami Warning - contact bom.gov.au

[Stephen Wilson]

Regarding tsunami amplitude, what really matters is the depth of the 
water where those measurements have been taken. 

I don't think there is much appreciation amongst lay people of how a 
tsunami operates.  It's very much like a set of ripples in a pond 
created when you disturb the water from beneath.  In deep water, a 
tsunami moves at amazing speed: many hundreds of km/h.  The amplitude is 
usually only a meter or so, and the wavelength many kilometres.  If 
you're in a boat on the open ocean. you won't notice them as they hoon 
past.

But when they encounter shallow water, they slow down, bunch up, and 
grow to tremendous heights that depend on the geometry of the near-shore 
sea bed and coastline. 

So ... it's hard to interpret the simple tables of wave heights and 
general locations, to give meaningful predictions of what happens at the 
beaches.  Maybe that's why the tables are described as for government 
agencies only?  For laypeople the figures look trivial and could be 
misleading.

Stephen Wilson
ex physicist.


Kim Davies wrote:
>> Agreed.
>> http://www.prh.noaa.gov/ptwc/messages/pacific/2010/pacific.2010.02.27.223924.txt
>>
>> Note that this link changes as more information is added. So far the 
>> wave sizes at the farther distances from the quake are below 1 meter.
>>     
>
> As the report pains to point out... "TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT." Presumably the waves would be larger than what those measurements suggest.
>
> kim
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