Don, a lot was being made of FFAs on this page...but Roger did an analysis (made graphs) and for M5+s there was nothing there...except maybe a hint of something at 102 deg or something like that. I forget exactly what Roger was running...but it may have been all M7 or 8 + quakes followed by all 5+ over 30 years......
For them to be real, they have to show up in an analysis like that. One could try it for a particular region with a complete catalogue for, say, M3+s.....

So, if I am fairly dismissive of them...it is because of that...do you have any hard evidence that they are real? What?
Chris