This is pretty brilliant if true. However, anything from PopMech has to be taken with a grain of salt. They are to science what the NYT is to journalism.

At any rate, a sea floor detonation of a 100 MT device could cause almost unimageanable devastation along absolutely vast segments of coastline. Think of the amount of uplift in a major subduction quake, meters maybe, now think think off an uplift of a couple miles or more that takes place in a few miliseconds. Tidal surges in the hundreds of meters could easily be expected.