## PSN-L Email List Message

Subject: Re: P-waves
From: Bob McClure bobmcclure90@.........
Date: Fri, 25 Mar 2011 11:42:11 -0400

```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 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
>
>
> At 03:57 PM 3/24/2011, you wrote:
>
>  Found what I was looking for ,,,,,  a animation of a P wave
>>>
>>
>> http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif
>>
>> notice there is NO vertical motion, it is totally longitudinal
>> P waves travel like sound waves do  :)
>>
>> cheers
>> Dave
>>
>>
>
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I disagree with yo=
ur hypothesis. Transverse motion is only possible with a wave of finite cro=
ss-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 ax=
is.

BobOn Thu, Mar 24, 201=
1 at 5:17 PM, Brett Nordgren <brett3nt@.............> wrote:

Dave,

I think in real world seismology, not everything always exactly follows the=
simple theory. =A0We see P waves quite well on our verticals. =A0For one t=
hing they are body waves and commonly approach the station from an angle be=
low the horizontal. =A0Also I think there is always a transverse motion ass=
ociated with compression waves like P waves--look up Poisson's Ratio. =
=A0I would normally expect them to have a transverse motion of very roughly=
1/3 the amplitude of their longitudinal motion.

Regards,
Brett

At 03:57 PM 3/24/2011, you wrote:

Found what I was looking for ,,,,, =A0a animation of a P wave

http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif<=
br>

notice there is NO vertical motion, it is totally longitudinal
P waves travel like sound waves do =A0:)

cheers
Dave

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