Glen....my casual (non quantitative)watching the California seismicty maps for about the last 18 years really makes it look like small quakes turn on and off state wide. Lacking large quakes to trigger these, it is not understood why this would happen. Or, I've never read a scientific paper that it does happen. You suggest that regions turn on and off. This may be very interesting if it can be documented in some kind of statistical way. Check with John V whether this sort of work has already been done and published...I don't keep up with this kind of literature. Lowell Whiteside, who used to post here, would be full of information on this sort of thing...it is in his Ph.D thesis for global..I think. You can get John to mail you his thesis if he doesn't want it anymore, or you can but the thesis. ..John may or may not say to not bother to buy it...Chris