The magnitude 8.0 earthquake of 19 September 1985 devastated Mexico City, even though its epicentre lay some 350 km away on the Pacific coast. Estimates of the dead range from about 10,000 to 40,000, with thousands of buildings collapsed.
The disaster was amplified by the soft former lake-bed sediments under the city, which trapped and magnified the seismic waves — a phenomenon known as site amplification. Buildings of a certain height resonated with the shaking and failed catastrophically.
The date became a turning point for Mexico: the country built one of the world's most advanced earthquake early-warning systems (SASMEX) and now holds a national earthquake drill every 19 September. Eerily, a second major quake struck on the very same date in 2017, deepening the day's place in the national memory.