I came across this app today and it seems quite apt for those living in Japan. Yurekuru is a Japanese Iphone app that sends out push notifications to your iPhone right before an earthquake strikes. It determines your location in Japan and will send out appropriate warnings for your location and specify the approximate occurrence of the earthquake in your location. You can set the warning threshold (because you would not like to be bothered with a low instensity quake would you?) as well. I set mine to 5 and up in the Japanese intensity scale. This is especially useful if your phone is not registered to receive warnings from the Japan Meteorological Agency.
Unfortunately its in Japanese, but can perhaps still be useful after you have a Japanese speaking friend set it up for you. It also gives you information on all earthquakes that occurred in all of Japan.