27 de agosto de 2014
Documento relacionado al Sistema de Alerta Sísmica como un ejemplo de éxito en Sistemas de Alerta Temprana para sismos.
Etiqueta: Mexico City
THE ECONOMIST EXPLICA CÓMO LOS MEXICANOS SABEN QUE UN TERREMOTO LLEGARÁ
28 de abril de 2014
The Economist explains
How Mexicans know when an earthquake is coming
Apr 27th 2014, 23:50
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?
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? Japan has something similar, and California is trying to put one together. But they generally give much less time to take cover than in Mexico. The reason is that Japan and California—and indeed most earthquake-prone places—sit right on top of faultlines, so earthquakes strike moments after the first tremors are felt. Mexico City, by contrast, lies hundreds of miles away from the nearest fault, meaning that it takes a minute or two for the wave to arrive. A place so far away from a faultline would never normally be vulnerable, but Mexico City is built on a former lakebed, giving it jelly-like subsoil which amplifies even tiny tremors into mighty window-rattlers. The strength of its early-warning system, therefore, is built on the weakness of the city’s foundations.
http://www.economist.com/blogs/economist-explains/2014/04/economist-explains-14
La revista Scientific American publica: “El temblor del viernes santo en la Ciudad de México probó la preparación de la región para un sismo mayor”
25 de abril de 2014
Good Friday Quake in Mexico City Tested Region’s Preparations for Bigger One
The city’s unusual geology allows engineers and seismologists to rely upon exceptional safety measures
Scientists can’t be sure exactly how much of a threat the Guerrero Gap poses to the hemisphere’s largest city. But they can begin to prepare.
Last week’s 7.2-magnitude Good Friday earthquake in Mexico City sent people scurrying out into the streets as chandeliers and other objects spun wildly in houses. The quake wasn’t Earth’s biggest Good Friday temblor (that was the Great Alaskan Earthquake of 1964), nor was it the biggest to hit on an April 18th (that was the Great 1906 San Francisco Earthquake). In some ways, however, it was more unusual than either of those, because Mexico City’s earthquakes are unique. Unlike other shaky cities, such as San Francisco or Tokyo, Mexico City is nowhere near a major fault. The nearest one is 200 miles away on the coast. Still, Mexico’s unusual rock and soil allow its residents to experience potentially powerful shaking. And while this has led to catastrophic events, it also provides unique opportunities to study earthquakes and prepare for the future.
Japan has a similar system in operation and California has tried for a decade to create its own (a new state law recently provided money for it). But because of Mexico City’s distance from its threatening fault, no other city offers as much of an opportunity for warnings. The signal on April 18 went out to 60,000 classrooms and the subway shut down before the quake arrived (and was running again just three minutes later). “It was a complete success,” says Juan Manuel Espinosa-Aranda, general director of SASMEX.
blogcires.mx 