My guess is that there is something happening that is triggering these periods of
activity/inactivity. It seems interesting to me that while Southern California was having
a strong quiescence northern California was having the strongest activity in months.
I have my own opinions on what may be triggering these episodes, which you know
very well, and I will not repeat again here. But a variety of factors may also be
involved. An excellent subject for future research - in fact I know of one person
at USC who is doing exactly that.
A statistical study would reveal if this is just random noise in an other wise
well behaved statistical system, but that is beyond me at this time.