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Magnitude 7.4 Earthquake Hits Southern Mexico

Mexico sits above a complicated system of tectonic plates that makes the region prone to violent temblors

A magnitude 7.4 quake shook Mexico's southern state Oaxaca June 23. (Xinhua/[e]STR via Getty Images)
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A large earthquake shook southern Mexico Tuesday morning. Mexico’s national seismological service estimated the earthquake at magnitude 7.5, while the U.S. Geological Survey estimated 7.4, the New York Times’ Kirk Semple reports, noting that early measurements can vary.

As of Wednesday afternoon, officials say that the earthquake killed seven people and injured about two dozen, while causing structural damage to several buildings, including to 21 hospitals, Kevin Sieff reports for the Washington Post. About 200 houses were damaged, and 30 were hit especially hard.

“We lost everything in one moment to nature,” Vicente Romero, an owner of a stationary store whose house was damaged in the earthquake, tells Reuters’ Jose Cortes. “This is our life’s work.”

The temblor hit the southern state of Oaxaca with the epicenter about 14 miles inland from the Pacific Ocean and 16 miles deep. The earthquake caused a tsunami warning and shook buildings as far away as Mexico City.

Far beneath Mexican cities, pieces of the Earth’s crust called tectonic plates meet in a complicated way. Specifically below southern Mexico, the North American plate slides over the Cocos plate at a rate of about 50 to 70 millimeters per year, which is “a gallop in tectonic terms,” Maya Wei-Haas writes for National Geographic.

That high speed shifting, combined with the fact that a ridge of crust that sticks upward is also being pushed under the North American plate, may mean that the area is especially earthquake-prone. The ridge might be causing increased friction between the plates, increasing the frequency of earthquakes, paleoseismologist María-Teresa Ramírez-Herrera of the National Autonomous University of Mexico tells National Geographic.

The region shows signs of large earthquakes from as long ago as 1537 and 1787. Mexico also faced large earthquakes in 1985 and 2017, when the country’s capital was hit by 8.1 and 8.2 magnitude temblors. In 1985, about 10,000 people were killed in the earthquake’s aftermath, and hundreds of people were killed in 2017. Per the Washington Post, Mexico revised its building codes in response to the disasters, but many major cities are still filled with buildings constructed prior to the updated codes that may still be vulnerable.

Mexico City also felt the effects of the most recent earthquake despite being about 300 miles northwest of the epicenter. Videos shared on social media show the buildings swaying in the city.

As Wei-Haas reported for Smithsonian magazine in 2017, Mexico City has unique geology that makes it especially prone to dangerous earthquakes. The city was built on top of an ancient, shallow lake, so it wasn’t built on stable rock, but loose sediments that move more like Jell-O when vibrations get trapped in them.

"It's almost like a bathtub, the [seismic] waves will slosh back and forth," U.S.G.S. seismologist Susah Hough told Smithsonian magazine in 2017. Rock, by contrast, shakes and crumbles.

This week, the state oil company Petróleos Mexicanos had to briefly shut down its refinery because of the earthquake, and almost two dozen hospitals suffered structural damage. Two of those hospitals were treating COVID-19 patients, according to CNN.

“Fortunately there was no major damage,” President Andrés Manuel López Obrador said in a video posted to Twitter early Tuesday afternoon, per the New York Times. In the video and others, López Obrador relayed updates from Mexico’s national coordinator of civil protection, David León, and other officials.

There had been “collapses, some broken glass, signage fell, walls, but nothing serious,” López Obrador said. “I hope and I wish with all my soul that there will be no more damaging aftershocks.”

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