Subject: Re: What's new on the tsunami front?

From: Alan W Harris

Submitted: Thu, 19 Dec 2002 14:09:02 -0800

Message number: 36 (previous: 35, next: 37 up: Index)

At 11:33 AM 12/19/2002 -1000, D. C. Jewitt wrote:
>Melosh's main point was that the ocean wave cannot be taller than
>the depth of the ocean, whereas some earlier work had allowed that
>possibility.  His second point was that the impact tsunami waves
>have a shorter wavelength than true deep ocean tsunami waves, and
>this allows them to break somewhat offshore.
>
>I think the first point is well taken.  The second needs more
>thought (at least on my part).
>
>Even taking Melosh's points into account, we are still talking about
>horrendously big waves.  Maybe not big enough to sweep across the
>eastern states to the Appalachians but NY and the coastal cities
>would all suffer.
>
>Would you prefer to be hit by a 16 wheel semi or by a GMC van?  That's
>the flavor of the issue at hand.
>
>Dave

Most semis have 18 wheels, the additional two are the steering ones in 
front, but without those, maybe a 16-wheeler would be even nastier.

Seriously, the issue is that according to Jay's "back of the envelope" 
calculation, the shore runup from "broken" waves would be less than the 
height of the diurnal tide, and thus essentially no more harmful than a 
typical storm swell.  We see the phenomenon Jay is appealing to with 
ordinary wind-blown waves.  A 3-ft deep water swell can become a 10 ft. 
breaker as it comes ashore, but after breaking, the "runup" on the beach as 
the wave surge comes ashore hardly gets above your ankles.

Our intention within the NASA group is to circulate a synopsis of Jay's 
claim to the various workers in the field (Ward & Asphaug, Hills & Goda, 
Crawford & Mader, and hopefully some real oceanographers that may know more 
about wave dynamics).  If those experts can't agree one way or the other 
then we will consider convening a workshop on the subject to see if we 
can't sort these things out.  However, in the short term I am busy 
concentrating on preparing my LSST poster for the AAS so I won't have 
significant time to devote to the tsunami issue until after the AAS meeting.

Cheers,

Al

*******************************************************************
Alan W. Harris
Senior Research Scientist
Space Science Institute
4603 Orange Knoll Ave.          Phone:  818-790-8291
La Canada, CA 91011-3364        email:  harrisaw@colorado.edu
******************************************************************* 


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