Few will hear of the Cocos

It was an event that flattened hospitals, schools, factories, high-rise buildings and much else: Mexico City’s 8-magnitude earthquake of 1985 killed an estimated 10,000 people.

This month history repeated itself, albeit with fewer fatalities.

An 8.1-magnitude quake in the south of the country this month – Mexico’s the strongest for a century – was followed, 32 years to the day after the 1985 quake, by a 7.1-magnitude event on Tuesday with an epicentre closer to the capital.

Mexico’s vulnerability stems from its location beside the Pacific Ring of Fire, where tectonic plates meet. Most of the country lies directly above the North American Plate, but to the south-west is the join to the Cocos Plate, while at its northwest, Mexico skirts the Pacific Plate.

The Cocos Plate is moving towards the North American Plate and is sinking beneath it, a process called subduction, which generates the stresses that cause earthquakes.

Seismologist Dr Stephen Hicks, from the University of Southampton in the United Kingdom, said both this month’s earthquakes were caused by the bending of the Cocos Plate.

“Once [the Cocos Plate] starts sinking, it bends under its own weight. The bending pulls apart some pre-existing fractures within the plate,” he said.

The 8.1-magnitude earthquake earlier this month was in an area where the Cocos Plate “gradually bends” as it is pulled under a thin layer of the North American Plate. The

Mexico City’s location makes it especially vulnerable to quakes, built on sand, clay and silt deposits left by water

AFP Different date but the same result – damage to the Hotel Regis, Mexico City, in September 1985. That year, 10,000 people were killed across Mexico in the 8.0 magnitude earthquake