Sounds like stress to me.. My ones do it for an hour or so following a water change (cold straight from the tap) and then come right, they did it for a day or so when I first got them too but it should pass really quickly..
I have found the shellies to be exceptionally hardy, even the fry, I tip them from tank to tank different temps and probably slightly different parameters and I am still yet to loose one so this is really confusing for me.
The only possible thing I can think of is the fish are just spooked and stressed from the quake and then aftershocks, no fish likes their house being shaken up. I would feed some of their fav food (some grindals if you have them mine go nuts for them) and/or add some schooling fish (I have rosy barbs with mine) to give them some confidence and see if that helps..
Hope they pick up soon!