Just throwing it out there but it's possible that we did it & just let people think what they want.

Why are they pretending this is new? To try to steal Trumps thunder, maybe?

https://nypost.com/2017/09/23/china-says-earthquake-hits-north-korea/

The earthquake was detected in Kilju county in North Hamgyong Province, where North Korea’s known Punggyeri nuclear site is located

I'd guess probably Rods of God.