I've mentioned this before and that is I have always noticed that when it comes to the greater LA area all the quakes trend and are related. Whenever the popcorn quakes start they seem to have a domino effect from Long Beach up to the Santa Clarita Valley. THEN one of two things happen, either they fizzle out (most of time) or you get 4+ quake as was case today. Most of the time it fizzles out but it should be worth noting that Norhridge was proceeded by a very similar pattern as this. I'm just an amateur, but I would be curious what an official scientist would think of this pattern.