At 7:18 in the morning Mexico city got a 8.1 magnitude earthquake, one of the strongest to ever hit the area. They effects were very bad because Mexico city is surrounded by mountains and volcanoes. The region was covered in lakes in ancient times to the city is on dirt and sand instead of bed rock and is very volatile during an earthquake. The earthquakes epicenter was located 50 km off the coast of mexico and 250 miles west of the city but unstable ground worsen the effects. Old hotels and factories made out of shoddy materials collapsed quickly and the tremors caused gas mains to break causing fires and explosions through out the city.
The mercalli intensity was IX (violent) and killed 10,000, injured 50,000 and made 250,000 people homeless. the average of 66-242,000 buildings and homes were destroyed in the earthquake. An aftershock hit on September 20 and had a magnitude on 7.5. The cost of the damage was estimated to be around 5 billion dollars.
Coco's plate subducton zone slid under the north american plate. Volatile trenches along the Coco's plate generally have had seismic events 30 to 70 years before 1985. However this particular section of the subduction zone had not had an event for a much longer time. Off the coast of Michoacan and Guerrero the earthquake caused a rupture in the sea bed 240 km long and 70 km wide, located between the subduction trench and the coast line. This is an inter tidal zone and the event caused widespread mortality in a number of species living in the area such as algae and shell fish.
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