[Physltest] [Phys-L] Re: earthquake

[Chuck Britton <cvbritton@EARTHLINK.NET>]

Water waves are a good example of the superposition of longitudinal
and transverse wave motion.


A wrong impression is given by this Tulane site by 'implying'  that
the tsunami consists of DEEP water waves while 'out to sea'.

It is important to note that the wavelength of the tsunami is GREATER
than the depth of the ocean. These are SHALLOW water waves that are
traveling across the oceans!!!!

Greatly different from both deep water waves and more normal shallow
water waves that are in 'actual' shallow water.

Deep water waves have an amplitude that is quite comparable to the wavelength.
A water parcel travels in a circular path composed of both transverse
and longitudinal mode.

The tsunami wave have an (vertical) amplitude that is a meter or less
and a wavelength of 100 km or so. The parcel path is very elliptical
until the depth decreases sufficiently to start the pile up of water.
Front of wave slows down while back of wave catches up and the flat
elliptical motion becomes circular and finally 'totally' vertical as
it climbs the beach.

At 7:12 AM -0600 1/3/05, Brian Whatcott wrote:
> At 08:20 PM 1/1/2005, I earlier wrote:
>
> > Here's a plausible description.   The current model of continental motion
> >    has it that plates of Earth surface move coherently.    They are motivated
> > in part by upwelling of material from the hot, more fluid depths. Where
> >    plate motion  encroaches on an adjacent plate, one or the other dives.
> > The subduction zone is not friction-free. An earthquake such as the one in
> > review presently, was reported to indicate a depth of about 10 km for the
> > origin of the tremor. One can easily suppose that elastic strain energy is
> > stored in the plate, until the latch in the subduction zone gives way.
> > At this point, one expects to see the plate edge move roughly as far
> >    as the upwelling zone has pushed the far edge of the same plate
> > since the last major slip.
> > The sound of your nails scratching on a blackboard has its counterpart
> >    in the 0.05 Hz fundamental 'squeal' of a plate moving on another.
> > There may be  theoretical justification for the talk of 30 meter drops
> > in a long slab of plate perimeter, or there may not be, but stick-slip
> >    motion of plate  boundaries is more or less a given.
> >    Nobody, I take it, would seriously doubt this as a cause for Tsunami
> > events.
> >
> > Brian Whatcott    Altus OK    Eureka!
>
> Here's a useful tsunami description from Tulane
>    <http://www.tulane.edu/~sanelson/geol204/tsunami.htm>
>
> Notice the snippet that offers that strike/slip alone
> is not necessarily sufficient for a tsunami.
>
>
>
> Brian Whatcott    Altus OK    Eureka!
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