The selection of an earthquake as the named disaster may have been made exactly because it is the least likely.

Use 'terrorist bombing' or 'tidal wave' and people might panic. And, of course, the always present conspiracy theorists would have a heyday speculating that the PTB know something, are expecting something, but aren't telling the public.

What happens if shortly after the drill there is an actual tidal wave or terrorist attack? The 'I told you so' chorus would be deafening. The truth that the named disaster for the drill was picked at random would get lost in the storm of public accusations and counter-accusations. The media could reliably be expected to 'document the controversy' and give credible sources and nut jobs equal time. Which means the average citizen, lacking the time to dig through the noise, is bound to be confused.

As it is the emergency services can't win for losing because picking the least likely disaster can be taken as a sign of ineptitude. Governmental/ bureaucratic ineptitude is a laugh line that never fails to deliver.

So it goes.