Absolutely RIGHT, Winquake does list PIS, but only in the Jefferys Bullen 
Table (1940).

I went to this site:
http://www.ucl.ac.uk/es/people/sammonds/3%20Seismic%20Rays%20Earth%20Structure.pdf
and only found that the small ( i ) means " Wave reflected at outside 
boundary of inner core (e.g., PKiKP)."  I did not find a direct reference to 
Pis, but it would seem that it is a P wave reflected off the inner core and 
concerted to a S wave.

WHY it would appear BEFORE the P wave is unknown.

Hope this helps someone somewhere............

Jerry 







Absolutely RIGHT, Winquake does list PIS, but only in the Jefferys =
Bullen=20
Table (1940).  
 
I went to this site:
http://www.ucl.ac.uk/es/people/sammonds/3%20Seismic%20=
Rays%20Earth%20Structure.pdf =20

and only found that the small ( i ) means " Wave =
reflected at=20
outside boundary of inner core (e.g., PKiKP)."  I did not find a =
direct=20
reference to Pis, but it would seem that it is a P wave reflected off =
the inner=20
core and concerted to a S wave.
 
WHY it would appear BEFORE the P wave is=20
unknown.  
 
Hope this helps someone somewhere............
 
Jerry