My experience has been that a 6.4 or 6.5 is the margin between a relatively non-destructive quake and something that collapses structures. A 6.7 is going to cause some things to fall down in Taiwan, while a 6.3 may not. Anything over a 6.0 is downright frightening, and even a 5.5 can scare the daylights out of me if I'm right over it.

From here in Kaohsiung, I rather enjoyed your recent earthquake! Nice, rolling action.

Other observations: The things that collapse most easily are unreinforced brick and any structure built on landfill.