There is a sharp line at exactly 100Hz, and whenever we measure this line, it reduces a lot if we put a sort of pillow below the (battery powered) vertical accelerometer. This should confirm that it's really seismic, and it is not induced by a magnetic or electric problem (however very unlikely with this configuration).
Strongest 100Hz signals are recordered on the platform. To be noticed that around the Detection Tower there is a scaffhold that mechanically "short-circuit" the platform with the tower's body.
Possible sources for the 100Hz seismic line could be ALL the front-end racks lying on the platform (about 10 mains transformers each one), but we need more measurement for a good hunt.
To be continued ...
