a whole lot of shaking going on

The floor underneath me has been shaking on and off since this morning.  My coworker thinks that it is from some nearby MTR construction or pile driving in a neighboring site.  I work at the Hopewell Centre in Wanchai.  If anyone can tell me why the ground is shaking I would really appreciate it.  I am feeling more skittish about it than I probably should and would like to ease my mind.