Because earth velocity increases with depth,  and seismic waves take the
"least time" path (simplification), P and S waves approach your seismometer
at near-vertical incident angle.  Since S waves vibrate perpendicular to
travel direction,  the ground motion is mostly horizontal. P waves have
longitudinal ("push-pull") ground motion, which is mostly vertical.

Hope that helps.

Jud
On Jun 7, 2013 1:37 PM, "Geoff"  wrote:

>  On 2013/6/6 11:35 PM, Dave Nelson wrote:
>
>
> Hi Jim,
>
> Now that little gem of info has answered the question I have had for years
>
> of course it now begs another question ....
> Why do P waves have a larger vertical component than S waves ?
>
> Dave
>
>
>
> SNIP......
> Now usually the P wave has more V  motion, so you might not get much P,
> from a Horizontal component.
>
> <<<    Jim
>
>  Also a question , Could it be somehow due to to the fact the S wave is
> side to side instead of front to back ?
>
Because earth velocity increases with depth,=A0 and seismic =
waves take the "least time" path (simplification), P and S waves =
approach your seismometer at near-vertical incident angle.=A0 Since S waves=
 vibrate perpendicular to travel direction,=A0 the ground motion is mostly =
horizontal. P waves have longitudinal ("push-pull") ground motion=
, which is mostly vertical. 

Hope that helps. 
Jud
On Jun 7, 2013 1:37 PM, "Geoff" <gmvoeth@.........> wrote:


 =20
   =20
 =20
  

    
On 2013/6/6 11:35 PM, Dave Nelson
      wrote:

    
    

      

      Hi Jim,

      

      Now that little gem of info has answered the question I have had
      for
      years

      

      of course it now begs another question .... 

      Why do P waves have a larger vertical component than S waves ?

      

      Dave

      

      

      

      
SNIP......

        Now usually the P wave has more V=A0 motion, so you might not get
        much
        P, from a Horizontal component. 

        

        <<<=A0=A0=A0
          Jim
    
    Also a question , Could it be somehow due to to the fact the S wave
    is side to side instead of front to back ?