Yep, this was caused from gravity. You can blame Newton on this one...G:
Along with the the jet fuel fire weakened floor joints pulling the walls in on the way down, right Geez?Those mean ol' evul turrists knew what they were doin'!
Yep Dad, I wouldn't so tall surprised but what there was a little magnetism involved. Dangit, there I go again talking about ism's...zzzZZ*Oh well, I believe in magnets. Maybe a solar flare presented a magnetic anomoly which possibly pulled in concert with gravity as the floor joints reached peak elasticity. Or another possibility is that maybe Arthur was smoking the joints?...(G: