alt Hacker NewsIt would seem the forewarning depends a lot on the distance from the epicentre. This quake, for Tokyoites, was far enough from them that they could beat the earthquake's speed. I'm fairly certain the people on the East Coast near the quake got no notification ahead of the event.
I was in a chat with people in NYC when it hit. They got advance notice, although it was just “why is everything shaking?” Followed by me going silent for a bit, so they didn’t know what was going on until it reached them.