From: henry@spsystems.net   
      
   In article ,   
   Gordon D. Pusch  wrote:   
   >I mis-remembered how long it takes for seismic waves to propagate through   
   >the Earth: Characteristic seismic wave velocities are actually in the range   
   >of 4--8 kps, so it will actually take less than an hour for P-waves (which   
   >are the fastest seismic waves) to propagate completely through the planet.   
      
   Bear in mind that normal seismic waves are *not* shock waves.  There is a   
   difference, and it matters in this case.   
      
   >Again, the amount of energy involved in such a large impact is so enormous   
   >that the seismic shock waves it produces will completely shatter the crust   
   >as they propagate through it...   
      
   Quite so.  And because shock waves alter the properties of the material as   
   they pass through it, they are *not* limited to the speed of sound in the   
   original material.  The speed of a shock wave depends on how energetic it   
   is.  Really energetic ones move much faster than the speed of sound.  The   
   speed of sound is the speed at which *weak* disturbances propagate.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
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