I found a partial answer
Posted by John Vidale on May 23, 2003 at 07:18:09:

Canie,

So "103's" are quakes following other quakes at the distance of the start of the shadow zone, and "140's" are at the end of the shadow zone. "most reliable following quakes of M > 7.5."

No word I could see on the reason this should be true, however.

John

Follow Ups:
     ● John, the rings come from Lowell - Roger Hunter  15:04:36 - 5/23/2003  (18779)  (1)
        ● but what's the logic? - John Vidale  15:28:57 - 5/23/2003  (18780)  (2)
           ● Re: but what's the logic? - Canie  17:30:57 - 5/23/2003  (18785)  (0)
           ● Re: but what's the logic? - Roger Hunter  17:29:53 - 5/23/2003  (18784)  (1)
              ● I'd expect a different pattern - John Vidale  17:51:33 - 5/23/2003  (18786)  (2)
                 ● Re: I'd expect a different pattern - Canie  21:52:51 - 5/23/2003  (18788)  (1)
                    ● Denali distribution of strong motions - John Vidale  22:50:14 - 5/23/2003  (18789)  (0)
                 ● Re: I'd expect a different pattern - Roger Hunter  18:40:47 - 5/23/2003  (18787)  (0)