a passing thought;
It seems to me a phase relationship
is responsible for steering of waves.
If you ever seen a phased array it
is a mass of feed horns and the phases
of the signals to the various horns are
altered electronically or fluidically or ?? by delay lines to steer the waves.
If you have a steady density or temp change
its like a delay line phase change which somehow
steers the waves back to the surface.
What we do with RADAR and other wave stuff is
simply using what mother nature already does.
So, do phase changes alter frequency,
or simply mean the phases change but the frequencies stay the same
when a large wave Trane passes over a variable density ?
It is interesting to compare and contrast what gravity
does to orbits and phase changes to to radio waves.
With the right density profile you might get
waves to travel in circles for a very long time.
????
It is hard for me to visualize since I'm not a physics/math person.


-----Original Message----- 
From: Mike Price 
Sent: Friday, March 25, 2011 9:41 PM 
To: psnlist@.............. 
Subject: Re: P-waves 

P-wave velocity increases with depth. This causes the wave paths to not 
be linear (and the wavefront is not spherical). The paths can be 
visualized as upward curving concave arcs. P-wave motion is therefore 
predominantly vertical when it reaches the surface at all distances from 
the epicenter.

Mike

On 3/25/2011 9:30 AM, Brett Nordgren wrote:
> Bob,
>
> I quite agree with your analysis. Some transverse motion would happen
> with an acoustic wave travelling down a steel rod, for example, but that
> assumes a free surface, which isn't the case inside the earth. The fact
> that the formula for the P-wave velocity uses the bulk modulus of the
> earth's material rather than its elastic modulus pretty well proves your
> case.
>
> However it is still true that P-waves will have a substantial vertical
> component, arising from the fact that the wave front will always to some
> degree be coming up from under the station.
>
> Thanks,
>
> Brett
>
> At 11:42 AM 3/25/2011, you wrote:
>> I disagree with your hypothesis. Transverse motion is only possible
>> with a wave of finite cross-section. A P wave has a more-or-spherical
>> wavefront and is not a beam of sound. Even a beamed wave would have no
>> transverse motion at its center axis.
>>
>> Bob
>>
>> On Thu, Mar 24, 2011 at 5:17 PM, Brett Nordgren
>> <brett3nt@.............> wrote:
>> Dave,
>>
>> I think in real world seismology, not everything always exactly
>> follows the simple theory. We see P waves quite well on our verticals.
>> For one thing they are body waves and commonly approach the station
>> from an angle below the horizontal. Also I think there is always a
>> transverse motion associated with compression waves like P waves--look
>> up Poisson's Ratio. I would normally expect them to have a transverse
>> motion of very roughly 1/3 the amplitude of their longitudinal motion.
>>
>> Regards,
>> Brett
>
>
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