Board Thread:Questions and Answers/@comment-10797017-20130624101208/@comment-11051098-20130712223743

It would be something like the effect of Yamajii's flames, like the effect he prevented when Wonderweiss' head exploded and all the flames he sealed away from Ryûjin Jakka were unleashed. Aizen stated the explosion would have wiped away the entire Fake Karakura Town and large surroundings if Yamajii didn't stop it.

So that could be the effect of a multiple-caster version of Ittô Kasô.