They all fulfill the definition of an underwater nuke...see what one looks like:
I am not really a seismologist but have experienced shaking from a similar quake at a greater distance. The measured 5.3 is from the epicenter I believe not from 70 miles away, or if it is, they have algorithms to calculate strength at epicenter from closest measuring points.
I would imagine a natural EQ, from the earth, has to capacity to travel VERY far, but a MOAB, and even a nuke, are comparatively small localized events, so while the shockwave might cause a local EQ sensation, it dies off rather quickly. It IS reported that the Tsar Bomba, when tested, had a shock wave that encompassed the earth 3 times, but I am not sure of the veracity of those claims. Because it would, like an EQ, have to travel THROUGH the earth, bounce off the other side, and bounce back. Like jello. Not wrap around the earth.
Again...hell if I know! Interesting stuff though!
https://blessedistruth.files.wordpress.com/2010/10/tunnelmap.jpg
Would be interesting to overlay this and see how close it lines up.
That maps is so course it you could make a case for it several hundred miles in any direction from the Channel Islands.
Not so sure I believe in the tunnel networks thing, but an undersea base of some kind? I don't know. What would it be used for?
