Played around with this in H DTK and H Utgarde Pinnacle over the past couple runs (King Dred and the undead troll guys near the boss that fear in DTK, berserkers in Utgarde)- there was a marked difference in fear uptime with three staggered tremors vs. one tremor. Still not anywhere near as reliable as when they were firing off once a second though.

Other factors may include range - I tend to spread out the sham in a standard cross patern, at 5-10yds apart, so it occured to me that 1 tremor down at one "point" of the cross vs. three down at the front, left and right points of the cross could make a difference as well?

If i remember this weekend I'll see about doing some more structured tests w/ logs.