we aren't near any significant tectonic activity and haven't experienced any significant activity in recorded history. there was a minor earthquake or tremor in cape town once.
thus the most likely cause of a tsunami would come from an asteroid splashdown.
the most likely cause of this would be the possible collision with apophis in 2030 odd, but that would only affect the west coast of the usa.
even then you need to bear in mind that of all the reactors in japan, given a direct tsunami and an earthquake and old technology, there were no deaths afaik.
if we were to be blindsided by and earthquake and tsunami big enough to take out a nuclear reactor, the nuclear fallout over the namib desert or mozambican channel would be the last thing to worry about.