Why does White Oaks Mall shake

I’ve wonder this for years now. Years ago when I was younger the shaking of White Oaks Mall was getting pretty bad. Area where it seemed to be most noticeable was by old Montgomery Wards store. Every once in awhile you can still feel a small vibration if your sitting in the food court. I think it would have been in late eighties when I remember seeing at least one person walking around with what I would consider a portable seismograph.

Was this Springfield Illinois mall designed to have some vibration? Is there seismic activity on the mall grounds? Is this 30 year old structure safe? I would assume so – considering vibration(s) have been going for as long as I can remember and nothing has collapsed yet. Still doesn’t make me any more comfortable when I feel slight tremor in floor beneath me while trying to enjoy a less than stellar selection of food. Not that I really travel into the mall all that much. Last time I sat in food court the vibrations of my youth could still be felt within floor.

Update 11/14/2018 Article that was linked below that contained information on vibrations testing was no longer working / available.

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