Yes, it is puzzling how this signal works and what is generating it. As I've mentioned before, a person who had a BS in Physics didn't know what was causing it either. Personnally, I don't think it has anything to do with the crushing of quartz crystals.

Lets see if I can draw a rough diagram of the how the signals act and the difference between near and far quakes which depends on magnitude or amount of energy being generated.
/\
---------------------- /\------------------- / \---/\---------/\------- <=The larger far away quakes or the smaller
/\ / \ /\ / \/ \ / \ close in quakes would be here
/\ / \/ \ / \ / \ / \
/ \ / \ / \ / \ / \
/ \ / \/ \ / \/ \
--- /----- \ /--------------------- \ /--------------------------- \ <= The larger close in quakes would be here
/ \/ \/

Hope this helps some.

Dennis