It 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.
Sorry? I don't get it. Why are you mentioning NYC? Was it a joke?
When the 2011 earthquake happened, those particular folks in NYC got a cryptic notice from me shortly before the shaking reached them.
I was thinking of the more recent quake which I very much felt and heard in my older detached home in Queens. I was in Farmingdale out in Suffolk during the 2011 quake. I got up to walk from my desk, took a few steps then suddenly became disoriented for a few seconds as if I was dizzy. Then my coworker shouts "Holy shit did you just feel that? That was an earthquake!"