Chris;

I looked at the Centennial Catalog, first for all great quakes and then for all from mag 5.0 to 7.9. I sorted out everything within +- 2 degrees and up to a year before each great quake and counted them by weeks.

I see no pattern in the results. Most had none, some had a few but not consistently near the big one.

The catalog is not complete at the low end and I don't know of one that is.

Roger