An enormous earthquake struck Japan about two years ago.
An enormous earthquake happened in Japan about two years ago.
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An enormous earthquake struck Japan about two years ago.
An enormous earthquake happened in Japan about two years ago.
An enormous earthquake struck Japan about two years ago.
An enormous earthquake happened in Japan about two years ago.
"happened": this merely tells us that the earthquake occurred.
"struck": this emphasizes the violence and suddenness of the occurrence, like a punch or kick.
not a teacher
The earthquake was not felt in every part of Japan (I don't think) so I would say that "happened" is fine if you just want to say what country it happened in. With "struck" I would be more inclined to specify the actual area which experienced the effects of the earthquake.