scale they use for earthquakes are a sliding scale big difference from 5.9 to 8.6
http://www.volcanolive.com/magnitude2.html
I was in MTB when the last large one happened,and was happy that local TV and authorites gave the evacuate call yes it was a bit crazy but better to be safe than sorry.
Dont know what the odds are of another wave hitting but must be in the millions more chance of being run over by Tuk Tuk in patong IMHO.