Chris,

I appreciate your comment and the emphasis on context. Looking at the thread, Mike was right in pointing out Cals lack of context. The subject of 4mag quakes is meaningless unless we pinpoint the fault structure involved. I also see on a different forum that the ETS - Episodic Tremor and Slip has started again up in the Cascadia Subduction. I have an idea that John Vidale will have some interesting insights on that in the coming months. And I will ask him about it.

You are also right about the M2's and M3's defining areas of rapid deformation.
The most notable example of this is the Anza Seismic Gap. The two on going swarms on each side of it are a good indication of the ultimate stress point. In my study of the two swarm areas, I found that there is a depth differential between the two areas. The south swarm runs deeper (12 to 20 km) and the north swarm occurs on average around 10 to 12 Km. I also see periods in the north that swarm at 7 Km. The quake occurance within each area is random, but when looked at macroscopically the swarms take on a greater significance.

I would say that any 4 mag quake in this area should raise the brow of any seismologist. Simply put, the deformation is outrunning the locked portion of the fault system. I'll put it this way. A 4 magnitude quake near the Anza Gap is a significant event. A 4 magnitude quake under Adak (on average)is not....

Glen