IMHO, for this topic, one starting point is to analyze the historic database and derive the so-called FFA regions per source location.

If the variances are low but the sample is small then, though this idea may give the appearance as having merit (in our short window), over time it may not be so well correlated (assuming that it is now...which is just an assumption {Has anybody done this study?..it seems so as the NEIC map of the world plots the shadow zone boundaries).

The idea of doing this per location is to see what variances may be happening in the FFA range rings. One might consider doing this since wave speeds vary over different regions of the earth (and assuming this is a factor if an FFA mechanism really exists). Also, the distances between major fault lines vary per "source" location (which when factored with wave speed variances may make a difference...or might by themselves?)

It may well be that the sample size is too small (per location too) to be meaningful, the FFA rings vary (somewhat or widely) from location to location, etc. and these considerations create enough large error so as to wash out any differences which may arise (or be attributed) due to the length of a rupture and where the most energy was found to have been released.

Now having said that, if pressed (and constrained to this context), I would say that an integration performed along the length of the rupture perhaps accounting for the relative angle of the FFA'd fault (to the source fault) may yield a better average FFA "shadow zone" range ring / activation angle. Each point along the source rupture may be treated as a point source of a given power level and, when integrated, could give an image of "received power" at a given FFA range.

When this process is automated, it might point to particular faults (at varying FFA range/angles per location) that just might show some activity as a result of some kind of FFA mechanism.

Since the regions where great quakes occur do not seem to be that numerous it may become obvious, upon review of the historical data, that any FAA mechanism may have stable FFA range rings (most likley effected {possibly}, one might expect, by the locations of major faults relative to each other...just a SWAG here....).

As an aside, it is interesting that 7 of the last 25 great quakes since 1973 have happened in the last two years. One might ask if human activity has any influence on these events. Do you think Daisy Cutters (15K bombs) dropped in Afghanistan contributed to any triggering of this last great quake?

FILE CREATED: Mon Nov 19 23:47:28 2001
Global Search Earthquakes= 25
Catalog Used: PDE
Magnitude Range: 8.0 - 10.0
Data Selection: Historical & Preliminary Data

CAT YEAR MO DA ORIG TIME LAT LONG DEP MAGNITUDE IEFM DTSVNWG DIST
NFPO km
TFS

PDE 1975 05 26 091151.50 36.00 -17.65 33 8.10 UKPAS 6D.. .T.....
PDE 1976 01 14 164733.50 -28.43 -177.66 33 8.20 UKBRK .D.. .T.....
PDE 1976 07 27 194254.60 39.57 117.98 23 8.00 UKGS .C.. ......V
PDE 1977 04 21 042409.60 -9.97 160.73 33 8.10 UKPAS 7C.. .T.....
PDE 1977 08 19 060855.20 -11.09 118.46 33 8.00 UKPAS .C.. .T.....
PDE 1980 07 17 194223.20 -12.52 165.92 33 8.00 UKBRK .F.. .T.....
PDE 1985 09 19 131747.35 18.19 -102.53 27 8.10 Ms GS 9CFG .TS...M
PDE 1986 10 20 064609.98 -28.12 -176.37 29 8.30 MsBRK .FFG .T.....
PDE 1989 05 23 105446.32 -52.34 160.57 10 8.20 Ms GS 5FFG .T.....
PDE 1993 08 08 083424.93 12.98 144.80 59 8.20 MsBRK 9CFG .T....M
PDE 1994 06 09 003316.23 -13.84 -67.55 631 8.20 MwGS .CFG ......S
PDE 1994 10 04 132255.84 43.77 147.32 14 8.30 MwHRV 9CFG .T....S
PDE 1995 04 07 220656.89 -15.20 -173.53 21 8.10 MsBRK 5FFG .T.....
PDE 1995 07 30 051123.63 -23.34 -70.29 45 8.00 MwGS 7CFG .T....S
PDE 1995 10 09 153553.91 19.06 -104.21 33 8.00 MwHRV .CFG ST....S
PDE 1996 02 17 055930.55 -0.89 136.95 33 8.20 MwHRV .C.G .T.....
PDE 1998 03 25 031225.07 -62.88 149.53 10 8.80 MEGS ..FG .......
PDE 1998 11 29 141031.96 -2.07 124.89 33 8.30 MEGS 7CFG .......
PDE 2000 06 04 162826.17 -4.72 102.09 33 8.30 MEGS 6CFG ......S
PDE 2000 06 18 144413.31 -13.80 97.45 10 8.00 MEGS .F.G .T.....
PDE 2000 11 16 045456.74 -3.98 152.17 33 8.20 Ms GS .C.G STS...S
PDE 2000 11 17 210156.49 -5.50 151.78 33 8.20 MsBRK .F.G .......
PDE-W 2001 01 26 031640.50 23.42 70.23 16 8.00 Ms GS .CFG .......
PDE-W 2001 06 23 203314.13 -16.26 -73.64 33 8.40 MwHRV .C.G .T....S
PDE-Q 2001 11 14 092610.01 35.99 90.50 10 8.10 Ms GS ...G .......

Looks like they are scattered around a little.