Some witnesses near the World Trade Center feel the ground shaking just before the South Tower starts to collapse:

EMT Joseph Fortis is heading across West Street, when, he says, “the ground started shaking like a train was coming.” He then looks up and sees the South Tower starting to collapse. [City of New York, 11/9/2001]

Lonnie Penn, another EMT, is outside the Marriott Hotel, which is adjacent to the North Tower. He and his partner “felt the ground shake. You could see the towers sway and then it just came down.” [City of New York, 11/9/2001]

Bradley Mann is at the EMS staging area on Vesey Street. He says, “Shortly before the first tower came down I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere.” [City of New York, 11/7/2001]

Battalion Chief Brian O’Flaherty is walking into the lobby of the Marriott Hotel. He says, “I hear a noise. Right after that noise, you could feel the building start to shudder, tremble, under your feet.” He then hears the “terrible noise” of the South Tower collapsing. [City of New York, 1/9/2002] Witnesses will also notice the ground shaking before the North Tower collapses (see Shortly Before 10:28 a.m. September 11, 2001).