Same as Japan, in many ways, but offshore nuclear detonation IS NOT RESPONSIBLE for what happened at Fukushima. Even though magnitude figures of 6.6 were measured just off the Fukushima coast and hundreds of aftershocks rolled in.
This $200 million 1971 test was performed to test an Anti-Ballistic Missile warhead, for a Spartan ABM missile. It consisted of a 5 megaton-yield thermonuclear bomb, detonated in a 50-foot diameter chamber, at the bottom of a 5,875-foot shaft (two kilometers down).
The blast registered a 7.0 on the Richter scale and caused a subsidence crater over a mile wide and 60 feet deep, which filled with water and became the largest lake on the island. Rockfalls, containing over 46,000 square yards of material, smothered intertidal marine life. Nearly three hundred deceased rock greenling fish were found offshore, and subsequent catches of rock sole declined substantially
The remains of over 10,000 three-spined sticklebacks and 700 Dolly Varden were found in the island's lakes, streams, and ponds. Perhaps 1,000 sea otters were killed, their skulls fractured by the force of the blast driving their eyeballs through the bones behind their sockets. Harlequin ducks were found with their backs broken and their legs driven into their bodies by the force of the explosion. [source Atomic Journeys - Welcome To Ground Zero]
The description and vast number of natural casualty figures in this 'test' made me weep.