Right when the guy in that last video said 'sugoi' is about when I said 'oh shit' and crawled under my desk. The amazing thing is that I sat at my desk for about 30 seconds beforehand wondering when this 'rather large' earthquake was going to start to slow down rather than escalate.
After feeling a lot of them, you start to be able to guess their distance and severity based on the P-wave vs S-wave timing of what you feel. It's kind of like counting seconds after seeing lighting until you hear thunder except you have 2 components:
Here's a matrix of the 6 big TV channels. Top left is the national broadcast (of the public broadcaster, NHK), the others are local commercial Tokyo broadcasts. The earthquake was initially not estimated to be big enough to affect Tokyo so Tokyo stations didn't automatically broadcast the initial alert. https://www.youtube.com/watch?v=eOrAwvJLKxo
