Manhattan is an island on a slab of bedrock: Tesla took advantage of that fact and the location of his old lab down on Houston St. to cause some heartburn for the folks within a 1/4 wave or so. The machine is very clever indeed but without the island it's not much of an earthquake machine. BTW, the actual device was quite a bit bigger and attached to a concrete pillar in the basement set into the bedrock.
Occasionally I would notice stuff mechanically ringing on the subway platform from big motors and whatnot in the buildings above. I remember once trying to point this out, it was a big barred grate I was leaning against that was shaking like James Brown. This girl thought I was a schizophrenic and ran off when I told her to put their hand on the grate to feel the vibration.
It never ceases to amaze me how, on some occasions, I can say the most outlandish shit and it will be swallowed whole without question, then at other times I can make factual observations with direct evidence at hand which is rejected outright and my sanity questioned.