National Seismic Monitoring Center
Tuesday 2nd July 1974
Just a quick note. I've had a good look at that GTSD, and to be honest, I have no idea what it is. It's unlikely to be some instrumental fault, since I confirmed our readings with both Utah and Nevada stations. It's hard to pinpoint the source exactly, but you're right about it coming from some military range, the BM Missile Range to be precise. We've had some strange stuff coming out of there in the past, but nothing like this. I'm under the impression that it's some kind of weapons testing facility, and we're getting echoes from some fancy new explosives they'd rather not tell us about.
I actually tried contacting someone at the BMMR, but they're remarkably secretive. The person I eventually managed to phone seemed to be unsure whether to confirm or deny the very existence of their workplace, so I doubt they'd be too forthcoming about top-secret weapons of mass-destruction.
Since, as far as we know, the Russians aren't involved, I suggest we just leave it alone and get back to looking for genuine nuclear detonations, not the unexplained. Spooky, eh?
Cheers, and enjoy the 4th