The people of Mexico City felt the ground shake several times onSeptember 19-20, 1985. Each (19.) tremor was a little stronger than theone before. A rumbling sound seemed to approach the city. The rumbleincreased to a roar, as if a huge train were rushing through a tunnel underthe streets. The ground rose and fell in waves. After the main shocks camea brief pause, followed by renewed shaking, the (20.) aftershock.