The Economist: How Mexicans Know When an Earthquake Is Coming T.W. - The Economist
go to original April 28, 2014

This video documents the health problems and relief efforts in the aftermath of the Mexico City earthquakes of September 19 and 20, 1985. The first earthquake (8.1 in the Richter scale) left more than 10,000 people dead or missing and thousands more injured. (pahopin)

Mexico City shook and rattled on April 18th, as a 7.2-magnitude earthquake sent people scurrying under tables for shelter. Tremors are a frequent scare for the city’s 20m or so residents, who experience dozens of small shudders a year. But the panic is lessened by the fact that people know the earthquake is coming a couple of minutes before the ground starts to tremble. Before this month’s big rumble, many Mexicans had already filed outside to await the wobble in safety, away from falling ceilings. Nowhere else in the world is able to forecast earthquakes in this way. How do the Mexicans do it?

In 1985 whole neighborhoods of the capital were reduced to rubble by an almighty 8.1-magnitude terremoto, which flattened buildings all over the city. More than 10,000 people are reckoned to have been killed. The damage was devastating: parts of the city have yet to be rebuilt. The impact on society was greater still. Some historians believe it contributed to the end of the hegemony of the Institutional Revolutionary Party, whose incompetence in the aftermath of the earthquake undermined its claim to be the party that knew best how to govern. The scale of the disaster, and the ineptitude of the official response, galvanized civil society like never before. Mexico City’s residents resolved that next time they would be prepared.

Within a few years they had come up with an ingenious early-warning system. The epicenter of earthquakes hitting Mexico City, which lies roughly in the center of the country, is usually to the south, where the North American continental plate rubs up against the Cocos plate. This means that quakes are felt first in states such as Oaxaca, on the Pacific coast. So seismologists installed sensors in the south of the country that detect the first tremors and send a warning to the capital. The seismic wave moves at about 7,000 miles per hour. That sounds fast, but it means that it takes the quake nearly two minutes to travel the 200 miles from Oaxaca to Mexico City. Meanwhile the sensors' signal arrives virtually instantaneously in Mexico City, where alarms are sounded, giving people just enough time to scamper out into the street before the earthquake arrives.

Why can no other country develop an early-warning system like this?

Read the rest at The Economist

Eduardo “Lalo” Salazar of Mexican television network Televisa quickly became an Internet celebrity when he remained calm and composed as a 7.2-magnitude earthquake hit the capital earlier this month. With the earthquake-siren blaring, Salazar kept his cool as he slowly and meticulously described what he was feeling and seeing. (Pedro Ferriz)

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