Hi Chris and John. There has been a question that has been running around in my mind for many years now. Up till now I have tried to find the answer on my own, but so far I haven't come up with an answer that I felt was the correct one.

It concerns large quakes. Those that are M>7.0 and larger and more often then now they will be on transform faults, but I suspect it could also occur on thrust and normal faults.

As I understand the mechanism of a quake is that it occurs whenever enough energy has built up to shear what ever is keeping the fault from moving at the location of the quake. Would it be possible for the area of the obstruction to be overcome by one plate moving under, over, or by one plate moving away from the other that would in turn allow the obstruction to pass one another? Not sure if I'm making myself understood so let me put it another way. You are at the base of a mountain. There are 3 ways to go around that mountain. Lets let the north side of the mountain is the up side and the south side of the mountain is the down side and going over the top of the mountain would be the 3rd way.

Could this account for why we have some foreshocks before a large quake that instead of the obstruction being sheared it is starting to slip past the obstruction by either going under it, over it, or around it? Going around it (over the top of the mountain) would cause the fault to separate at the epicenter of the quake? Sure hope you understand what I'm trying to say. Take Care…Don in creepy town