Hello All;

I understand sound waves have convergence zones
due to the fact that sound is lazy and always
bends in the direction of slowest velocity.
also it will reflect nicely wherever the
velocity profile quickly changes.

Sound will travel down then bend up and hit the surface
then reflect back down again only to be refracted
upward again and again in concentric circles
around the transmitter thus the shadow zones.

This convergence zone behavior of vibrations
was known to geologist before it was to
SONAR peoples or so I understand.

These surface vibrations do not travel in a straight
line like the initial P wave through the EARTHS core.

It is all very complicated and Im sure requires
fitting the math to the actual structure of
the earth since the Earth is not homogenous.

You may find general maps showing this behavior
but most likely not the complex model.

Since it is of military value in monitoring whatever.
The military is quite good at fitting the math to
collected intelligence and thats basically what its
all about to model reality.

I have seen these maps before but not relating to
any specific geographical area only to an
average.

The best we can do is the ttim program offered by the
USGS where you put in your location and get in return
the various phase times.

This used to be the place:

http://neic.usgs.gov/neis/travel_times/artim.html


FYI

geoff



----- Original Message ----- 
From: "GPayton" 
To: 
Sent: Thursday, September 17, 2009 9:15 AM
Subject: Re: Shadow zone


> Thanks to you Randy and Dale.
> 
> CONFESSION:    I am a dunce, but I do not see what you and Dale previously 
> sent about Great Circle Mapper.  Inserting MY coordinates and a given 
> distance only displays a circle of that given distance with me as the 
> center.  Everything outside that distance surely is not in the shadow zone. 
> Perhaps, I do not know what the magic distance should be?
> Jerry
> 
>  ----- Original Message ----- 
>  From: Randy Pratt
>  To: psn-l@..............
>  Sent: Thursday, September 17, 2009 10:45 AM
>  Subject: Shadow zone
> 
> 
>  Here is a link to a great circle mapper.  You can put in coordinates and 
> generate a world map with your location and concentric cirles at any desired 
> distance.  I have done mine for each 10 degrees out to the shadow zone and 
> then again from the far side of shadow zone.  I just set this image as 
> wallpaper for my desktop for quick reference.
> 
>  http://gc.kls2.com/
> 
>  Randy 
>
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