Tremors

I was on the line commenting on the Jazz Festival with Mr. Koshy last Friday and we noted that the floors of 1 Borneo shook..more like a mild earthquake kinda tremor..this was when the crowd was dancing in front of the stage. It's not like the vibrations we sometimes felt (I've experienced at Centre Point, Karamunsing etc) but really shook. Anybody care to shed some light on to this? Mind you the crowd was not as many as you might see in clubs or discos..