According to a 9to5Mac tipster, iOS 5 in Japan will include notifications from Japan's earthquake early warning system. It ties into iOS 5's Notification Center, and can be enabled and disabled just like any Notification Center section in Settings. Because it stays connected to Japan's nationwide online monitoring network, it will most likely lower battery life slightly, but given the importance of the system, that's likely a tradeoff anyone enabling it will be more than willing to make.

No word yet on whether any other earthquake-prone, or natural disaster-prone areas with early warning systems of their own will be able to likewise tie into Notification Center, though App Store apps can fill that gap where and as needed.