Seismic simply means very, very low frequencies, like 5Hz down. And it is no boogey man, they are quite real. Ask anyone who has put the Townshend Audio Seismic products (or perhaps Geoff’s springs) under his speakers, turntable, CD player, or tube electronics if they are effective at providing isolation from floor-borne vibrations (which transmit up into a speaker cabinet or an equipment rack, and through a turntable’s suspension, none of which provide isolation at seismic frequencies. That is why the microscope isolation tables selling for $2000-3000 sell as well as they do to those of sufficient means). There are a few here on Audiogon, one in Portland who has invited me over to hear them under his speakers for myself. I already own the older Seismic Platforms (used in conjunction with roller bearings, effective down to around 3Hz), and will be adding Pods shortly.
Again, Max Townshend has an excellent video on You Tube in which he explains and demonstrates his Seismic products. It is definitely worth a half hour of one’s time to watch.