I live in Japan, and have done since well before the 2011 quake, and can only second the above comments.

If travelling in earthquake country, do your best to be aware of your surroundings, e.g. know where emergency exits/staircases are, have an idea of the general layout/geography of the local area, read up on any disaster information relevant for the region. Carry cash (power/internet may be down and all the magical modern payment methods will be useless) and some sort of ID (passport or passport copy) with you where possible. Personally, when out and about in Japan, I always carry a small flashlight as I will want to conserve my phone's battery, and one of those insulating foil sheets in case I need to spend the night somewhere inconvenient, and some candy'n'stuff. Also a paper map in case I need to walk home - assuming mobile communications are available, they will be hopelessly overloaded; this was the case in 2011, and also last year when an earthquake knocked out the power in the Tokyo area for several hours. If you do experience a large earthquake, it would also be a good idea to try and send a short text message / email / chat message to anyone who might be concerned about you, telling them where you are, your current situation etc.

If near the sea, consider the possibility of a tsunami (if in Japan, and shortly after an earthquake you hear sirens going off accompanied by urgent-sounding announcements, drop everything RIGHT NOW and go as high as you can as fast as you can, either high ground or third/fourth floor of a solid building; do not attempt to flee by car).