Maybe solar cycles, there has been increases in geological activity in the past during these solar cycles.
Any Geology types out there who can add to this would be appreciated, I am struggling for a correlation/causation.
Maybe this?
The mystery of the ‘rumble in the Indian Ocean’: Strange seismic waves that shook the world...
Daily Mail UK ^ | 11/29/2018 | CHeyenn Macdonald and Harry Pettitt
http://freerepublic.com/focus/f-chat/3709249/posts