[meteorite-list] LANL: Meteor Could Cause Big Tsunami

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Wed Jan 12 14:08:05 2005
Message-ID: <029301c4f8da$04dc9360$f551040a_at_bellatrix>

No argument that we should have tsunami monitoring systems in every ocean.
And such systems might even provide data about ocean impacts that happen
fairly often and are sub-tsunami producers.

BTW, the last estimate I read suggested that the actual plate movement for
the Indian Ocean event may have involved a vertical shift of 8 meters over
an area 1000 km long by 100-200 km wide. That is a massive volume of water,
and in terms of energy alone is much greater than that produced by a
mid-velocity, 1 km diameter impactor. And the earthquake coupled 100% of its
energy into the water, whereas an impactor would couple only a small
percentage.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Sterling K. Webb" <kelly_at_bhil.com>
To: "Meteorite-List" <meteorite-list_at_meteoritecentral.com>
Cc: "Chris Peterson" <clp_at_alumni.caltech.edu>
Sent: Wednesday, January 12, 2005 10:43 AM
Subject: Re: [meteorite-list] LANL: Meteor Could Cause Big Tsunami


> Hi,
>
> I don't see how I could be making fun of Los Alamos by citing a work by
> J.
> G. Hills of the Los Alamos National Laboratory! I wasn't making fun of
> Gisler's
> work, either. I was being querulous about the newspapers.
> Of course we could wait years? decades? for the perfect simulation. Or
> better still, since they're just simulations, wait for the impact to occur
> and
> then just measure the devastation. But I thought the purpose was to
> evaluate
> risks, and you can't do that without an estimation of the risks.
> Only the Pacific ocean and the nations surrounding it have a working
> tsunami
> sensor and warning system. We have seen the result, in the Indian ocean,
> of not
> having such a system, which might have cut the number of deaths in half.
> It's inconceivable to me, considering the very low cost of such a
> system,
> that there should be none for the north or south Atlantic ocean basin
> either.
> This is because the seismic risk is considered negligible (just as it was
> in the
> Indian ocean).
> But I think it is necessary to try to assess impact as one of the
> possible
> tsunami risks. You're quite right that the calculation is a very murky
> one,
> though.
> As for the water displacement, Chris earlier wrote: "There is some
> question
> about the dynamics of the water displacement- that is, most of it goes up,
> not
> out. And that total volume of water is somewhere between a few tens and
> few
> hundreds of cubic kilometers. Contrast that with the recent Indian Ocean
> event.
> The shift in the ocean floor resulted in the displacement of over 1000
> cubic
> kilometers of water, and produced waves in most locations of 3-5 meters."
> Water waves do not consist of water moving in the direction of wave
> motion.
> They consist of water oscillating at a right angle to the direction of
> wave
> motion. So water in a wave is never forced "out," only up-and-down.
> As every ten-year-old intuitive physicist knows, the best way to make a
> water wave is with a good ker-plunck!
> In an "ideal" water wave (infinitesimal particles, frictionless fluid)
> ALL
> motion is vertical, i.e., transverse to the vector of the wave's
> propagation.
> The wave propagates; the water does not.
> In a "real" water wave, the surface is composed of small cyclindrical
> cells
> which revolve as they go up and down, producing a small surface motion in
> the
> direction of propagation. This produces a small frictional loss which will
> eventually cause the wave to die out (after many thousands of kilmoters).
> It's only when a water wave interacts with a boundary (shoreline) that
> the
> kinetic energy of that vertically oscillating mass is suddenly transformed
> into
> horizontal motions, with devastating effects.
> An impact that produces up-and-down motion is the perfect way to create
> a
> wave. The seismic event in the Indian ocean was a thrust slip, in which
> one
> plate of the earth's crust was forced upward by a few meters (less than
> ten)
> over a broad area (few hundred sq. km.).
> This up-and-not-down motion seems to have translated perfectly into a
> water
> wave of about the same height as the plate displacement. (Since water is
> imcompressible, this is pretty much inevitable.)
> Personally, I think a low-altitude airburst of an small incoming object
> would more efficiently produce water waves than is generally appreciated,
> and
> represents an underestimated risk.
> Now, to find a simulation to prove it...
Received on Wed 12 Jan 2005 02:07:53 PM PST