Abstract
It happened suddenly, and the results were devastating. A major earthquake (Richter 8.1) shook Mexico City on September 19, 1985. The tremor which lasted about four minutes caused the collapse of over 250 buildings and the deaths of thousands. Ironically, many died in two large hospitals that had collapsed. Thirty-six hours later, a second tremor (Richter 7.5) caused further damage of upright and toppled buildings. The total number of badly damaged or destroyed buildings from the two quakes was estimated at 2500, and the number of deaths was expected to exceed 8000.