The warning to America about nuclear retaliation if Tsunami are used as a weapon against the eastern Han cities should be taken seriously. I believe the Fuku Shima incident was a proving test that went very well.
SEALs will now be best deployed every few months checking for devices around the Azores, Canaries and undersea mounts that are faulted, in the Atlantic and Pacific.
These may be detonated by design, with coinciding natural disasters elsewhere in the USA. This will maximise damage, minimise notice and hope to be lumped into the same category as a natural series of events.
Clathrate deposits will be used to maximise water displacement. Detection of these devices, buried near or under explosive methane will be problematic.
The military might of America may then be unleashed, but where will be the proof? Gather it now and tell the Han!