First, only 2 countries have bombs near that yield, 140 megaton, the US, Russia just under that with Tzar.
Korea's little poppers, perhaps 6 kiloton, about like our MIRV tactical nukes, say 5 times Heroshima.
Out in the Atlantic, probably just a dull thud on sonar. Some fallout after.
I was 60 miles from the test site when they detonated a 140 megaton device, just did swish a little water in a glass.