Mexico is in the worst possible place for earthquakes — here's why it keeps getting hit

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February 17, 2018 3:03 AM

Mexico sits atop three of the Earth's largest tectonic plates, and its soft soil — home to a former lakebed — amplifies the tremor from earthquakes.

A 7.2-magnitude earthquake struck Oaxaca on Friday evening.
The quake comes just months after another powerful and similarly sized quake hit Mexico City.
The country sits atop three of the Earth's largest tectonic plates.

If giants were playing a game of Jenga with countries as their table-tops, Mexico would be one of the last locations to get picked.

The country sits atop three of the Earth's largest tectonic plates — the North American plate, the Cocos Plate, and the Pacific Plate. Whenever these chunks of crust grind or butt up against one another, earthquakes happen. As a former lakebed, Mexico City is also home to soft soil that essentially acts as an amplifier for tremors, often making smaller earthquakes feel much larger.

On Friday, a 7.2-magnitude quake struck Oaxaca, according to the US Geological Survey. The epicenter hit the town of Santiago Ixtayutla, but tremors were reportedly felt as far as 350 miles away in Mexico City.

The temblor comes just five months after a 7.1-magnitude quake hit Mexico City, nearly on the anniversary of a deadly magnitude 8.1 earthquake 33 years ago which killed more than 9,500 people. That repeat quake reverberated along the boundary between the Cocos and the North American plate as the southern-most plate slid beneath its northern neighbor and struck roughly 3 miles northeast of the city of Raboso.

Mexico is one of the most seismically active countries in the world.

Over the past century, the country has seen 19 earthquakes within 155 miles of the epicenter of last year's earthquake, according to the US Geological Survey. Earthquakes aren't the only local hazard, either — the region is also repeatedly subject to volcanic eruptions.

South of the 2017 earthquake's epicenter, two volcanoes — El Chichón and Volcán de Colima— erupted in 1982 and 2005, respectively. Two other active volcanoes southeast of Mexico City called Popocatépetl and Ixtaccíhuatl occasionally vent visible gas, and the former erupted most recently in 2010.

Much of Mexico City is built on a former lakebed, where soft soil has been found to intensify the effects of earthquakes.

A paper published shortly after the area's 1985 earthquake found that the shaking had been amplified by as much as 500% in regions near the epicenter where the soil was the softest. Since then, the city has taken some steps to manage the risk from future quakes — such as updating building codes near the capital and launching an earthquake early warning system — but many parts of the country still suffer from a lack of safe infrastructure.

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