In a message dated 20/01/2008, rpratt@............. writes:

I see the shadow zone has a range of definitions from 102 to  105 as 
beginning and 140 to 142 as ending depending on the reference.  Is  there a most 
accepted range or is it somewhat dependent on location?  Is  it a sharp cutoff or a 
gradual reduction over a few  degrees?


Hi Randy,
 
    The shadow zone is due to the large dense core of  the Earth 'shadowing' 
the signal transmission. The core refracts P waves, but it  will not transmit 
S waves directly. You also get some variation due to the depth  of the quake. 
The cut off is gradual. 
 
    Regards,
 
    Chris Chapman



   






In a message dated 20/01/2008, rpratt@............. writes:
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  it a sharp cutoff or a gradual reduction over a few=20
degrees?

Hi Randy,
 
    The shadow zone is due to the large dense core=20=
of=20
the Earth 'shadowing' the signal transmission. The core refracts P waves, bu=
t it=20
will not transmit S waves directly. You also get some variation due to the d=
epth=20
of the quake. The cut off is gradual. 
 
    Regards,
 
    Chris Chapman