Dennis - I think they would give some sort of warning - They were concerned about the Hector Mine quake triggering a San Andreas quake and they did get public announcements out - granted the state made them tone down the warning (so don't blame the geologists). I think if they were very sure and it was a warranted warning we'd hear something.

Also after a largish shake they talk about percentages of a larger one to follow and how it goes down with time. I just hold my breath in that first 24 hours! (and the china)

Canie