User blog comment:Xilinoc/Ch. 563 - SUPERSTAR NEVER DIE/@comment-1706259-20131227165911/@comment-11051098-20140102222938

If Aizen could generate an explosion from the lowest level of Muken, it would have made more sense if he did so before. The captains meeting room is in the 1st Division barracks, so why not blow up the building during a captains meeting, given that he could feel their reiatsus and know when they were all in there?

I understood it the way that Yhwach created the explosion. Or what if he had Bambietta do it? Seeing as she can turn objects into bombs by firing her reishi into them - shooting reishi into the 1st Division building and BOOM.