realism - Why didn't the bomb cause a tsunami in Dark Knight Rises? - Movies & TV

As far as I know, even smaller earthquakes measuring 4.2 on the Richter scale in Japan have triggered tsunamis. Was the atom bomb used in The Dark Knight Rises not this powerful?

Answer

First it was 4.2 on Richter scale. 4.2 M_W is just unit of energy.

I don't think the bomb would have caused a tsunami though - it may have caused huge waves but they wouldn't have reached Gotham.

The Bomb was capable of destroying 6 mile radius area. So assuming that bomb was dropped 6 miles away from Gotham in the ocean, the water would have absorbed much energy and say the effect would have been reduced by an additional 1 or 2 miles. (The energy is constant, the effect of exploding in water doesn't make a difference)

Also I would like to quote from this article from Geology in Motion:

This means that the power of the tsunami along that shoreline was about 1.3 *10^12, or 1.3 petawatts.

^{(1 petawatt is 109 M_W or (1000000000 M_W), easily many times the bombs dropped in Hisroshima and Nagasaki combined.)}

And this was the energy of the waves at the coastline in Japan, Just imagine the energy at the point where it was created.

Although I accept the effect of nuclear explosion under water would have been very serious as it would have caused the entire water to get contaminated by nuclear radiation. All marine life would have died in many mile radii and still thousands of people would have been affected.