Neat idea, but the math is all wrong...
The amount of energy expended to not only move that much earth, but also move that much water is ENORMOUS! Even larger than the explosion of the
Tsar Bomba (50 mt). So the nuclear device would have to be enormous as well, even with modernized
technology.
On top of that, why hasn't anyone reported an increase in radioactive material in the water? Why are there not signs of radiation poisoning in the
people, plants, animals, etc in the near by regions? Why did none of the nuclear blast reporting satellites pick up the blast? On top of that, how did
they manage to drill the enormous bomb to a depth of 30 km (18.6 mi), which was the depth of the epicenter of the quake, much less under all that
water? How could they transport a bomb that size to the location? How could the hide all the infrastructure needed to go with the bomb?
I can go on here, really...