Alfredo Estrella/Agence France-Presse via Getty Images
ALFREDO ESTRELLA/AFP/Getty Images
By Adam Taylor | Washington Post
Late Thursday, Mexico was shaken by an enormous 8.1-magnitude earthquake that struck off its southern coast. At the time of writing, the death toll is at least 32 people.
Mexican authorities have called it the largest earthquake in the country in 100 years. Data from the United States Geological Survey shows more than 40 earthquakes in Mexico or just offshore with a magnitude of more than 7 in the past century, but just four with a magnitude above 8.
The most notorious took place in 1985, when an 8-magnitude earthquake hit off the coast of Michoacan state. That earthquake ended up causing chaos in Mexico City, the country’s highly populated capital, with a death toll ranging from 5,000 to 40,000 and thousands of buildings severely damaged.
That earthquake sparked major political change in the country. Many were incensed by the lackluster response of the long-ruling Institutional Revolutionary Party (PRI) to the disaster, and real political opposition formed to challenge Mexico’s entrenched one-party system, ultimately leading to the PRI’s ouster in 2000.
Going back further, there have been earthquakes of even larger magnitude: One quake that took place in 1787 had an estimated magnitude of 8.6 and caused a tsunami along 310 miles of the coast that swamped areas as far as 3.7 miles inland, though it produced few deaths in an area that was then sparsely populated.
As a country, Mexico is particularly vulnerable to earthquakes: The country is in a region where a number of tectonic plates butt up against each other, with huge amounts of energy waiting to be unleashed. The epicenter of Thursday’s quake was near where two plates – the Cocos and the North American – collide. USGS notes that within 155 miles of this area, there have been eight other earthquakes with a magnitude of higher than 7.
Mexico City itself is also unusually vulnerable to earthquakes. A 2008 blog post by Horst Rademacher of Berkeley’s Seismology Lab explains how the problem goes back to the Aztecs, who founded their capital, Tenochtitlan, on an artificial island in the middle of a shallow lake in the region’s central plateau. The lake was later drained and the city became Mexico City, but the core vulnerability of the site to earthquakes remained.
“A lake bed in a basin [ . . .] is one of the worst grounds for constructing a building,” Rademacher wrote. “While hard rock simply shakes with the same frequency and amplitude as seismic waves, the unconsolidated sediments of an ancient lake bed react differently: They can amplify the shaking and even worse, they can lose their consistency and become a liquid.”
The 1985 quake made obvious the risks posed by this factor, as many buildings simply collapsed as the ground shifted beneath it – despite the fact that the earthquake was centered more than 200 miles away.
This week’s quake doesn’t appear to have caused considerable damage in Mexico City, though it was felt there and caused some electricity failures and other damage. The capital has implemented a variety of measures since the 1985 quake to try to limit potential damage, including a seismic sensor system, warning sirens and significant changes to building codes to strengthen new structures.
Other parts of the country may be worse hit, however, and it might take some time to know the full extent of damage in remote areas.