Check the vicinity
It is not as though earthquakes are constantly happening in Japan, it is just that they are more frequent statistically. Being slightly more aware and prepared is thus advisable, but the precautions don't need to be excessive. One thing however to keep in mind is where you will go in the event of a major earthquake and water and power goes off. All areas all over Tokyo and other cities will have designated earthquake retreat zones. These are generally in school yards, large expansive parks, by rivers, or on major thoroughfares. Here, people will gather to await instructions from safety officials, and of course get access to water and shelter if necessary. In all honesty, the earthquake would have to be absolutely massive to warrant leaving your home to a shelter zone, but it's good to keep in mind when in Japan.