Bob,

I have never heard of a Pb phase, either in regional or teleseismic
studies. I have no idea what Winquake is doing.

The Pn, Pg, and P* phases all arrive within a few seconds. Suppose an
event is at 100 km from the station: Pn at 7.76 km/sec, arrives about 12.9
seconds after the origin time. Pg at 6.5 km/sec arrives at 15.4 seconds,
and P* at 5.6 km/sec arrives at 17.9 seconds, or 5 seconds after Pn.
At twice the distance (and time, of course) Pg and P* often fade out.

The classic reference is: SEISMOLOGY, by K.E.Bullen, Cambridge Press,
Third Edition, 1965.  He describes the early efforts to determine near
regional velocities in the '30s.

As regional networks became reliable in the early '70s, a more complete 
picture of the near regional structure brought out papers in the BSSA 
by Nuttli, Kisslinger and others, but the original terms of the 1940's 
J-B tables were retained. Unfortunately, I don't know of any specific
references. Maybe the annual indexes of the BSSA would mention some
papers, or maybe the Seismological Society has a searchable data base.

Regards,
Sean-Thomas
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