Tokyo-Yokohama Information Source

The horrible E-word is earthquakes. To many of us Japan offers a quality of life, especially security, which cannot be matched elsewhere. But the one thing which gives many of us jitters and which would make us leave this country is the thought of a major earthquake. Sure there are dangers and risks elsewhere in the world as well but the thought of the "pending" earthquake can make many paranoid. I recently read that Japan is the first country in the world to install early warning systems for earthquakes which will give people a few seconds (Shizuoka 10 seconds, Nagoya 25 seconds and we in the Tokyo area 40 seconds - don't know why there is such a time difference though) to put out the fire and get under cover.
What I heard is that the early warning will be given via radio or television. But what if you don't have either of these sources of media on at that time? Would warnings be given via the public announcement systems installed on some streets? Is there "warning" announcement which Gaijins like me - who don't understand much Japanese - should learn? Considering how much noise pollution there is in this country, especially from the police cars, ambulances, the garbage collectors, the sweet-potato sellers, the unwanted applicance collectors, the local council announcers, etc., how does one make sure the announcements being made are serious? I know an old man a block away from me who once told me if there is an emergency he will come looking for me to warn me. But the 10 minutes he needs to get to my place may be too long in the case of E-word.