Should this phrase not include a comma: "O, mavi mavi kanepede oturdu" as in in "O, arabayı durdurdu". In the latter, the comma was explained as being there to distinguish between the pronoun he/she/it and the adjective that. Therefore, wouldn't O mavi kanepede oturdu translate as he/she/it sat on THAT blue sofa? If not, then would it be O, şu mavi kanaep oturdu?
I too am learning Turkish, so don't take my word. However, I assume this is the reason:
O mavi kanepede oturdu -> Implies location, not motion. Therefore, the locative is used. The focus is on the (stationary) act of sitting.
Neden buraya oturdun? -> Implies motion, insofar as the emphasis is on why you SAT DOWN, not why you sat down THERE. The focus is on the transitory action of sitting DOWN.
I'd be interested to see if any experts can weigh in on my suspicions!