I really don't understand why someone with 500 Giga to 1 Tera hash/second hashrate would attack the TRC network instead of making a load of money mining BTC. Note that this attack has gone on for many days now, while BTC has gone all the way to USD$250 and beyond. So instead of making up to $5,000 mining BTC everyday, this person is screwing around with the TRC chain and got maybe 50K~60K TRC coins, worth only $10,000 at the current exchange rate. So the person basically spent $30,000~40,000 in lost opportunity cost to attack the TRC chain. That frankly is not rational.
Something that makes sense is if the individual has a mega ton of Bitcoins from the oldschool days (millions of dollars worth). That person can afford the opportunity cost of not using the ASIC to mine for bitcoins. And that person has an extremely strong incentive to stop competing coins eating into the market share of Bitcoin.