If I read Wiki correctly, looks like the warhead is 2 megaton or so.
That could put a serious downer on the day.
The Christmas day earthquake 2004 was a 9 plus richter scale Earthquake that unleashed thousands of megatons of equivalent energy that produced a large destructive tsunami over a wide area but never a 1600 foot high one. Same for the recent Japanese Fukyama(sic?) earthquake and tsunami.
I suspect a device could be rigged to do major damage to say NYC but due to vaguaries in geology , depth, and other factors the device’s impact would no doubt be limited...I doubt such a device could destroy a 3000 mile coastline. They wouldn’t need to....a drone could just pop up in a harbor close in to a target city and the nuke in it could go boom.
The whole story when i first heard of it sounds fishy like so much vaporware. No one has ever tested such a weapon nor could they ever test it even once in friendly waters to see if it would actually work as fabled. The testers would destroy themselves.