There was a belief that a braahmana who went out of Aaryaavarta (the piece of land lying between the Ganga and Yamuna rivers, that is) became a "jaathi bhrashta" (fallen from caste) and had to perform purificatory rites before being accepted back into his family and the caste. This belief possibly got broken when the brahmins spread through out the subcontinent. Similarly there was a belief that a braahmana crossing the sea became a bhrashta and had to do purificatory rites after returning to Indian shores when only he would become an unpolluted brahmin, once again. This belief also has gone down the drain because the ruling principle is udaranimittaṃ bahukṛtaveṣam or, earning a livelihood is the most important thing in one's life!
Now, coming to Tarpanams, the idealmost braahmana is supposed to perform 96 Tarpanams in every year, and one year of ours is supposed to be equivalent to one whole day for the Pitrus (Uttaraayanam being daytime and Dakshinaayanam, the night). We perform the annual Sraaddham on the same tithi as in which death occurred and if this tithi is sometime during the month of Aippasi, then we are feeding a full meal by waking up our said Pitru at dead of night! In addition, we are giving them water to drink 96 times during their whole day & night duration. If our pitrus have human characteristics then their entire life would be in complete misery, having to eat at any odd time of night and having to drink 96 cups of water daily!
You may form your own decision about doing Tarpanams abroad.
