How to isolate turntable from footstep shake or vibration

I find it amusing that you are doing exactly what you infer I am.😄 👍

Townshend Seismic sink or wall-mounted (assuming solid rather than plasterboard walls)

MC, You might be correct about the cause of the bridge collapse. I mentioned it more for the sake of humor than anything else, and my guess is or was that the resonant frequency of the bridge suspension(s) and the wind velocity had something to do with it. But I certainly did not back up my remark by actually researching the cause. If you look at the famous video of the bridge shaking itself to death, it appears that the suspensions, one on each side of the bridge expanse, are resonating at different frequencies, which causes the road bed to be twisting and tilting so crazily, which eventually led to disaster. I dunno.
Anyway, we all agree that putting a turntable with a built in spring suspension on top of a spring-suspended shelf is usually not a good idea, unless the doer has a good understanding of the physics and the proper instruments to determine what might work.  This is not a knock on spring suspensions per se.

Matter of fact that is exactly what I recommend doing, putting the spring suspended table here on top of a Townshend Podium or Platform. Don't know which Oracle we're talking about here and I'm not familiar with their suspensions either. But all we really need to know is the one we have here isn't isolating from people walking around. A Podium definitely will accomplish that.  

The only real questions are how bad does the OP want to eliminate this, and what is he willing to do? A massive rack like mine will just about do it, and it is very inexpensive to make. But it is incredibly massive (well over 500lbs) and a time consuming DIY project. Townshend Podiums will definitely do it, and improve all aspects of sound quality as well, but does cost a lot more especially as it will have to be pretty big, those Oracle have a big footprint!   

The most cost-effective answer will be if the Oracle feet can be replaced with Pods. Some turntables like Basis this is easy and the way to go. But Oracle half the turntable is about how it looks, so I don't know.....

It is picking up the footfalls because it is amplifying the octave that the turntable suspension system is moving at and affecting so you will need to wall mount the table and use an appropriate shelf to wall mount it with there are some very good wall shelf choices.