The earthquake early-warning system by the meteorological agency in Japan actually tells us about an earthquake BEFORE it hits. It's becoming very useful (and annoying, it pops up during tv programs and the show gets postponed for a while) these days when aftershocks are becoming an everyday thing.
There was a quake at school today too, but that actually wasn't an aftershock, it was another different one.
What does an earthquake alert look like? If you're living in Japan and is watching where there are people, you'd better warn them this isn't the real thing so they won't panic.
All the people in the diet are like "w..w..wh..what??"
The alert combines a lot of discords, so it sounds something terrible.
that's the point.
Even if we're just turning on the tv as a sort of a background music, this leaps to your ears, screaming for attention. And so you get up and go under a desk or something.
How does this system work?
It's done by catching the P-wave, a very weak wave coming from the epicenter when a quake occurs. Though it's weak, it's a lot faster than the very big S-wave, so technically the big S-wave comes after the P-wave.
And when you catch the P-wave, calculate the epicenter and VERY QUICKLY put it on tv and radio, everyone can at least have a few seconds before it starts shaking. Big deal? You don't know what a few seconds can do. You can get under a desk or something to save yourself. And I think it's pretty big that we get ready for the quake in an emotional way. It's better than being hit without notice at all.