Why isn't the kinetic energy going into the upper block to crush it, arresting the process? ... Don't tell me it's because the block fell - when it hits a floor, the impact energy is also transferred upward.

By that logiv, we should expect <symmetric crushing of floors both upwards and downwards of the original structural failure, with the top uncrushed floors moving at a faster and the crushed floors at a slower speed downwards, both accelerating, and certainly no arresting of the process. What would then arrest the process would be a floor that could absorb all the energy and momentum of the floors upwards...

Since I can't access the link, I don't know what exactly the authors claim as sequence of floors crushing.

_{*Lunatic*, n.
One whose delusions are out of fashion.}