[arianvanp]

Could I trade with that btc on both forks at the same time?

[brazzy]

After the fork you have 1 BTC which you can use only on the BTC chain, and 1 BTH which you can use only on the BTH chain. And these are completely separate.

[zodiac]

Think about it using my definition of fork, the answer should be clear

[veli_joza]

I wouldn't use expression 'protocol upgrade', that implies it's mandatory and that current protocol is rendered obsolete. I think 'fork' better explains the mechanics.