How to isolate turntable from footstep shake or vibration

I just suspended my audio rack, not the 70 pounds power amp, from the ceiling with ajustement screws, and a foam insert to the bottom to prevent excess of mouvement.

My experience with a "VibraPlane" isolation device was that it not only isolated a turntable from the sub-sonic problems mentioned by the OP, but that even the placement of other equipment, like a CD player or DAC produces a surprising improvement in clarity and focus. I understand that they are used with electron microscopes to improve the clarity of the images. There seem to be quite a few used ones for sale on EBay from about $400 to $4000. It works, but they are HEAVY !!

@lewm, the Russians used tubes in their military avionics until the mid 70s I think. You would think just looking at a tube with it's delicate appearing insides that it would be sensitive to vibration. Is this reality or lay instinct? I use a tube phono stage which uses 6922's. It is not the tiniest bit sensitive to vibration, at least as far as I can hear and I have done some pretty crazy things. I have 25 foot long RCA interconnects from my Krell amplifier days so we put my turntable and phono stage on top of a subwoofer just for fun and to prove that the Sota was impervious to vibration. I had no intension of testing the phono stage. But, tonearm interconnects are only so long so the phono stage went with the turntable. I'll bet you can guess the results. I think the high end was slightly rolled off but my brain would think that anyway because it knows to much about the effect of length on single ended interconnects. Otherwise, everything sounded exactly the same as before I moved the turntable set up. But again this was subjective and only an indicator.  I have never seen any proof that tube electronics are sensitive to vibration. If you have seen some I would love to see it. As far as what people hear?  Subjective evidence is an indicator. It does not rise to the level of proof. Lay instinct is a horrendous trap I think most of us have fallen for at one time or another. I certainly have which is probable the reason I treat these issues more cautiously. I am not about to go out and spend money on an anti vibration platform for my phono stage. I have no reason to.

Do what I did - move to a residence built on a continuous slab......silent as a tomb. Of course, the motive of the move was not to exorcise demonic vibration hobgoblins from my stereo systems, but it was a factor in my decision to buy this particular town-home that is now mi casa. My Thorens TD 160, 160 Super, and TD-320 have now been rendered impervious to the vagaries of heavy footfalls.....the only worry is that a cat might decide to use one of the 'tables as a trampoline while it's playing.

I am also surprised @mijostyn that you doubt that a vibration platform would help with your phono stage.

What you don't seem to comprehend is that in addition to external vibrations, there are internal vibrations within components that can be drained with a good sub platform. Regardless of a slab or whatever. In these cases, you can get a multi layer platform instead of springs or podiums or whatever. From what I was told, SS is even more susceptible to this than tubes. 

Not so much on a turntable, so I buy the SME lack of need of vibration control. Also, the biggest beneficiary of vibration control is a CD player, even more that turntables for some reason.

Don't ask me, just ask Peter at Symposium Acoustics who has been doing this for 29 years.