I have also found this information possibly related to the question in New
Zealand Journal of Geology and Geophysics.  "For a focus at the surface, the
Jeffreys-Bullen tables demand an origin time some three seconds earlier: and
one or two seconds earlier for a focus near the base of the granitic layer.

 

I also found a reference to PIS involving a slab-mantle-interface reflection
with slab-face P-reflection velocity contrast upwards to 10 percent.  This
appears to pertain to the Japanese subduction zone. 

 

Both of these require purchase of documents so I can not get more detail.
Perhaps they will give a clue to the questioned phase.  

 

Randy














I have also found this information possibly related =
to the
question in New Zealand Journal of Geology and Geophysics.  =
“For a
focus at the surface, the Jeffreys-Bullen tables demand an origin time =
some
three seconds earlier: and one or two seconds earlier for a focus near =
the base
of the granitic layer.

 

I also found a reference to PIS involving a =
slab-mantle-interface
reflection with slab-face P-reflection velocity contrast upwards to 10 =
percent. 
This appears to pertain to the Japanese subduction zone. =


 

Both of these require purchase of documents so I can =
not get
more detail.  Perhaps they will give a clue to the questioned =
phase. 


 

Randy