I don't know...but the Earthquake Storm idea, based upon stress transfer, is a good candidate for this. Has been showing some promise in other areas, but alas I have been out of the field for tooooooo long!

It always surprises me that California had 3 very major quakes from 1857 to 1906, and not much since then. I know, I know...the term MAJOR depends very much on whether or not you had your house destroyed or family members killed. Our biggest destroyers so far in the last 100 years have been in the 6 plus range, and we've been lucky with the 7 pointers being located away from population areas.

Or, as Lucy Jones once said "Earthquakes tend to happen where earthquakes are happening."