With all of the fault lines and not so stable areas in California....all the way up to Canada, I would think the last thing needed would be explosions of any kind underground or near the ocean. ELQ, would it not leave any kind of residue or signature...either prior or after? I am not a chemist, but you would think there would be trace elements left...this is for all areas of unexplained explosions. There sure seems to be lots of them!