🚀 go-pugleaf

In article <CKAMAw.Kpp@netnews.jhuapl.edu> Robert Jensen
<jensen@aplcomm.jhuapl.edu> writes:

>In article <1994Jan26.184923.4533@TorreyPinesCA.ncr.com> Max Stern,
>lms@TorreyPinesCA.ncr.com writes:
>>This accords with and explains my own personal experience.  I live in
>>Sherman Oaks, and it happened that I was on the phone with people as
>>far as ten miles away during several of the larger aftershocks.  Within
>>a fraction of a second, we both announced that we were experiencing an
>>aftershock.  At first, I thought this was incredible, since the wave
>>has to take finite travel time, and I was thinking in terms of the
>>speed of sound.  Then I read an article in the paper which cited the
>>very high speed of the S wave, which -- together with Richard's point
>>about "phase velocity" of the spherical wavefront's intersection with
>        ==============
>        
>I think that this should be the "group velocity".  No energy or
>information moves at the phase velocity.

But that's exactly the eternal paradox of phase velocity!

>
>>the surface -- makes the near simultaneity of its arrival at distant
>>points quite understandable.

I'm an amateur here... what is the definition of "group velocity"?
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 |  | /   \ /\                      Max.Stern@TorreyPinesCA.ncr.com