I wonder if it has something to do with the resonant frequency of the building. This is one of the reasons that you don’t march an army over a bridge.
That’s quite possible.
If a group of exercisers can induce such strong vibrations in a building, I’d be very concerned about the building stability. I wonder if they are having engineers examine it?
South Korea had a huge building boom a while back. I’ve seen other stories where the developer couldn’t get enough rebar but had to meet deadlines, so they put the building up anyway.
There was the shopping mall which collapsed a few years ago there. There was another massive project where they were putting up enough apartments for 300,000 people. In both cases the developers went to jail.
I’ve felt buildings shake before due to people. The floors quiver in parking garages as cars go by. This sounds to more pronounced.