[TrainedMonkey]

I can't find any reliable sources, so treat this as my own speculation. I heard that there were programs for a while in two big countries with acronyms starting with US that aimed into exploration of causing earthquakes/tsunamis that would hit across the word by using multiple underground nukes and constructive interference.

[tedks]

There was an American program towards the end of the second world war aiming at causing tsunamis to weaken Japan: https://en.wikipedia.org/wiki/Tsunami_bomb

[FranOntanaya]

I would suspect this was more for propaganda effect -- local populations would understand better a threat if it was related to something devastating they actually had experience off.

[icelancer]

Certainly reasonable to believe. Those countries were exploring literally any and all avenues to undermine the other.