I'm not a physicist but as I understand it, the shockwave of a nuclear blast can account for 50% or more of a nuclear blast's energy. This shockwave, as well a

I'm not a physicist but as I understand it, the shockwave of a nuclear blast can account for 50% or more of a nuclear blast's energy. This shockwave, as well as the fireball and thermal emission are all linked insofar as they're all caused by a massive amount of X-rays vaporizing the bomb and rapidly superheating the atmosphere near the bomb. These X-rays predominantly come from the energetic collisions of fission products and the fission itself. AFAIK that building survived not because nuclear blasts produce weak shockwaves, but rather because it was a very strong earthquake resistant building in the first place, and because it handled being loaded from above well (concrete and brick generally handle compression well.) If it had been a bit further to the side, I think it might not have remained standing.