Which place is more safe? Well, when you think of it both are equally dangerous, especially if you are in a place where Tsunamis are frequent!
A Tsunami is rare, yet the Tsunamis, when they happen, can cause massive amount of damage. They happen when an earthquake underwater occurs, this send a massive wall to form, this wall breaks in two and sends waves in all directions.
Before a Tsunami hits, make sure to be in a sturdy building, if not, find high ground. Make sure to also warn others if you see one. I haven't seen one yet though.
While a Tsunami hits, you should have supplies, for example, a First Aid Kit, Flashlights, Batteries, and a Clean Food and Water Source. I'm just happy there is not ONE Tsunami coming.
If you get hit and are swept away, you will probably die, but I didn't because I'm a fake character. But when one really hits, wait it out and after don't explore until rescue teams arrive.