What happened
On the morning of 19 September 1985, local time, the subduction zone off the Pacific coast of Michoacán ruptured. Yet the worst damage was in the capital, more than 350 kilometres away: the soft sediments of former Lake Texcoco beneath the city centre amplified the shaking and set mid-rise buildings resonating. At least several thousand people died – estimates reach 10,000. After the disaster Mexico built an earthquake early-warning system. Exactly 32 years later, on 19 September 2017, another destructive earthquake struck the capital.
How to read these data
Magnitude measures the energy released at the focus: each step is about 32 times more energy, so an M 9 earthquake releases about a thousand times more energy than an M 7. Its effects, however, also depend on focal depth, distance to cities, ground conditions and building quality – a shallow M 7 beneath a city can be deadlier than a deep M 8 under the ocean.
Data: USGS ComCat (usp0002jwe) · Wikipedia (pl) · Wikipedia (en)