The blast was so loud it woke people as far as three miles away, triggering thoughts of a plane crash or earthquake. Alex Pflanzer was sound asleep when his home’s windows blew out and his wife started screaming. What he didn’t know — what nobody knew Saturday night about an hour before midnight — was that something had caused an explosion that leveled at least two nearby houses in this middle-class Indianapolis neighborhood so far south that it’s almost a suburb.