I wrote a program to find all the quakes of a given size or larger, compute the interval in years between consequtive events and count the results.

I ran this against the Centennial Catalog and found that you can get all sorts of answers depending on the miniumum size you allow.

But in no case did I find an excess at 56 or 9 years.

The 56 wouldn't do well anyway, with a 106 year database but the 9 year would show up if there was one.

Roger