On 29 Aug 2003 13:10:55 -0700, (Art Unwin KB9MZ)
wrote:
I was thinking that it showed a particular high
resonance ( mechanical? ) at that particular point
but that is what I want it to represent.

Hi Art,

It appears that Peter's references offers a form of math to satisfy
your observation:
William C. Elmore and Mark A Heald, "Physics of Waves", first published in
1969, but
most recently published in paperback by Dover Publications, New York, 1985
and
generally available in reprints even today for around US$17.00. A real
bargain.
ISBN: 0-486-64926-1 LCCN: 85-10419.
or
With compressive-dillutive waves
the "vibrations" occur in the effective density of the medium.
....
B. L. N. Kennett, "The Siesmic Wavefield", Cambridge University Press, New
York, NY, 2001. ISBN: 0-521-00663-5.

But be aware it is full of gratuitous partial differential equations and
tensor analysis. The stress-strain variables of compressible-dillutive
media are expressed as tensors and the partial differential equations are
cast in tensor form.

73's
Richard Clark, KB7QHC