Is an explosion moving slower at/near the center than at the outer perimeters-ie the blast front?

I used to ume that all ges in an explosion moved out at the same velocity, & that the ges kept rushing over all parts of the "blast zone". I started questioning that until I watched Trinity & Beyond, a doentory about the history of nuclear tests. What I was surprised by was the footage in the damage radius. I watched buildings & other large objects get blown over, only to see the rapid flow of debris stop (immediately), then I saw the sign of the often pointed out backflow-pressumably from the gasses elastic nature. Am I to assume that the event that slammed the structures was the SHOCK WAVE, & not the BLAST FRONT? I can see possibilities either way. I know that shock wave & blast front are NOT the same thing, but I CAN see why a blast front can exibit an identical property. An outrushing outer blast from an explosion exerts an implosive force towards the center of the explosion, in an exchange of pressure & velocity. I also know about-& have witnessed (on film)-the elastic nature of gasses in an explosion over-expanding, & "snapping back". You could say it's about the anatomy of an explosion.