Is the basement safe during a tsunami

If the basement is around 6 meters deep?

Higher ground is the only safe place during a tsunami bececayse the amour of water thy flows onto surface can be enough the break down the basement door that is either inside or outside also water can seap in if their are cracks anywere is the walls roof door ect

If you live in a place that is subject to tsunami and there is a tsunami early warning system; once activated, you should seek high ground, away from the coast; not a basement.
If you don't have such a tsunami early warning system, it doesn't matter, it will be over you before you can do anything.

Please, understand that your risk to get harmed by a tsunami is extremely minimal, even if you live in a place that is affected by them. Ask your friends if they know anyone who died in a tsunami. Then ask them if they know anyone who died in a car accident. Still, we are driving cars every day, right?

Incidentally, I have a friend who died in the Thailand tsunami, a few years ago. The irony is that he was an excellent sailor who sailed so often single-handed, here in Norway, at any season and in any weather. Faith was such that he had to die from a monster wave when on holiday in Thailand.

No basement is 6 meters deep. That's over 20 feet! And any place where a tsunami could be a threat, the land is at or near sea level, so no house would have a basement in the first place due to a high water table.