Good questions. The discussion so far on buffer zones is too simplistic.
Waves in water are mathematically interesting - the longest wavelengths
travel fastest, and the shorter wavelengths get damped out more by
friction (try dropping a stone in a pond). After all, the tide is a
moon-synchronous wave, which depends on the fact that the phase speed of
a wave with a wavelenght of half the circumference of the Earth is close
to the rotation period of the Earth. So the 2004 Indian Ocean Tsunami,
by the time it got to the Maldives, was much more like a tide. In many
places the sea level rose and then fell gently - in the Met Department,
the PCs which were on the office floor were flooded, but the TV camera
on its tripod was unharmed.
When waves come into shallow water, the wavelength shortens and the
phase speed decreases - that is why waves on a beach end up parallel to
the beach even if they start off as a significant angle. Also the height
of the wave increases, so a gentle swell in deep water can produce large
waves on the beach. When the anglular height of the wave decreases below
a threshold, the wave will become turbulent (breaking) which dissipates
some of the energy. Also there will be focussing by the shape of the sea
bed and the coasts.
Hence the effect of a tsunami on a land mass is not easy to predict, it
will need detailed modelling. The characteristic of the waves will
depend on the distance and direction from the original displacement, as
well as reflection from other obstructions. It could even be that reef
areas around an island would increase the turbulence and hence the
friction, and be more damaging to structures on the island than a
laminar flow.
I would much rather be in a boat in deep water! If the water was deep
enough, and you were far enough from land, you would probably only
notice the wave by taking detailed measurements of position, height and
speed.
Stephen Palmer
Technical Co-operation Programme Manager
Met Office FitzRoy Road Exeter EX1 3PB United Kingdom
email: [log in to unmask]
phone: +44 (0)1392 886915
mobile: +44 (0)7771 808531
fax: +44 (0)1392 885681
http://www.metoffice.gov.uk
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