I figured it was probably natural. There of course is or was the possibility that it wasn’t.
This is a wild place. If you’re into that sort of thing (I am), look on You Tube for multiple volcanic eruptions, Kamchatka. The one I’m thinking of was a helicopter flying over.
Wiki has this page about Kamchatka earthquakes
https://en.wikipedia.org/wiki/Kamchatka_earthquakes