Roger:

Re: rectangle/trapezoid - You could calculate a north and south corner distance and then average them to get a better "circular equivalent"...if you wanted to improve the accuracy in this area.

RE: Oblate earth and distance formula - Curious...what is it (if it's not too much trouble to post) ?

RE: 10% extended range used vs actual candidate quake range - I hope you'll consider putting in the option to use the candidate quake distance...since any extension outside the predicted range is more or less arbitrary ....
A bias arises when using this in a low versus high seismic area (where there are more quakes and where the probability appears higher).

Re: Largest quake = best fit. - From a technical definition the best fit is that which most closely matches the predicted parameters...though I understand the discussion about using the largest quake.

Good point about mentioning the fact....

Anyway, as long as the same program is run on all predictions I think it will definitely indicate who's doing well and who is not. As you know, there may well be differnces of opinion as to how each calculation should be done, etc. However, your program looks like a good effort at making progress in this area (especially in a more automated fashion). WTG (Way to Go...)

$.02