I'm not sure where the ring idea originated, but it looks like it is in Whiteside's thesis starting at page 119. I have the thesis (thanks Lowell) and for a change just spent 5 minutes looking for this. On p. 119, Lowell says that amplification in"all three data sets at 17 deg, 25 deg, 34 deg., 60-61deg, 71 deg, 102-105 deg, and 144deg and within 2 deg of 180 deg (the antipode). Canie-are these the distances in the FFA maps? I know 102-105 is, and that is supposed to be one edge of the shadow zone. In Fig 31 on the next page there are graphs showing correlation. Then, there is a comprehensive table. Etc. As to the validity of these correlations, you would be the better judge-I'm not a statistician, nor am I a seismologist. However, as a research scientist, and knowing your interests a little, I recommend that you get an original copy of his thesis on interlibrary loan and read it. I actually did read the whole thesis in 2000. I say original copy because those printed from microfilm are a bit hard to read. The problem with Lowell's thesis is he basically trys everything. But, if he is half correct on 20% of his stuff, then there is good stuff in there. I personally, but not quantitatively, think that there may be a relatively weak but real effect that can be brought out as statistically significant by use of large numbers of quakes-and Lowell really is an expert on earthquake catalogues. Chris