There have always been earthquakes in Korea. They are just typically quite weak. Though the south region that is closer to Japan has experienced some intense ones, but nothing like the massive ones they have in Japan.

Never has been: https://en.wikipedia.org/wiki/List_of_earthquakes_in_South_K...

The entire Pacific region was full of volcanoes already. It's not a place you want to go if afraid of tectonic activity.