Glen, pray do tell what the Elsinore Enigma is. I can guess, but I have not heard of it: guess: trenching shows it is Holocene active, but no big historic quakes?
Bob&Glen...they can look at the rate of fault loading from modeled GPS and look at the rate of Moment release from quakes and see if there is a deficit. However, they also have to take into account that some of the motion may be taken up by non-seismic processes (pressure solution for example).

There was a paper in 95, Dolan et al, I think in Science, that said that Southern California had a large deficit and that there should be lots of M6s to make it up, or rarer M7s. But, later papers by others said it was not true. I probably can find one or 2 of the later papers in my files.
Chris