In the event of a major disaster, relevant emergency information will be broadcast by radio (as well as on TV, and online newspaper updates, so it is worth taking note of the following stations:
AM Radio - AFN (American Forces Network) – 810 kHZ in the Tokyo area –

FM Radio –
Bay FM – (78.0 MHz).
FM Cocolo (76.5 MHz) – (Kansai area) –
Inter FM (76.1 MHz) – (Tokyo Metropolitan area only) –
J-WAVE (81.3 MHz).
NHK FM (82.5 MHz)
Tokyo FM (80.0 MHz).