And how do you cover the thousands of miles of coasts, the thousands of small fisher towns, how do you protect the propertises, etc?
And image, for us big cities people, that they find out, let's say four hours earlier ( being very optimistic ), than a major earthquake is gonna happen near, say, afar from New York, resulting in a tsunami that'll hit one hour later. Let's assume they decide right away the decision is accurate, that the info can be prepared and broadcasted in a flash, etc. ko, now, imagine, live broadcast in New York: " People, in 5 hours, a tidal wave 10 to 20 meters high will hit the city". No matter how diplomatic will be the tone used, it will result in only one thing: chaos. Everybody will try to run for their lives, but nobody will get out.
So the US west coast has an advanced warning system? I suppose it has yet to show it's usefulness. As for japanese, they're used to that, I suppose they would react right away, w/o any need for special warning or anything anyway.