I have no words for disasters like the recent Boston Marathon bombings. Which means that I prefer to call them atrocities rather than tragedies.
I don't mean to nitpick but I'd rather stick to the semantics of the senseless than the cathartic. I'm not going to get any effect out of trauma and try to squeeze it into a useful or manageable meaning. Trauma and atrocity, after all, are those events that we can never master.
Call them atrocities. Horrors and fears.