>>64140645 (OP)
Guam and Hawaii aren't going to sink themselves.
A few megaton class thermonuclear devices capable of altering geographies should do it.
Chinese are long term planners. They know that an enemy will rebuild a city in a few hundred years after it getting nuked. So they require a solution that prevents a population center to reappear by turning a land feature non-existent in the first place.
Kinda like how the Roman depopulation and salting of Carthage prevented the reemergence of another powerful city state from appearing in North Africa.
