Canie,
I have noticed a pattern similar to the one you describe too, but usually
involves an unusual quake off the coast of So. California. I have never done
any statistics on it, though, so am not sure it is not just coincidence. We
remember after a significant quake other things that happened before. These
things may always be happening, but our attention is drawn to them when
a quake occurs. Patterns like this are hard to quantify. Any suggestions on
statistics for this, we have the whole catalog at our disposal.