Terremotos

THE EARTHQUAKE OF SEPTEMBER 19, 1985

Mexico is a country whose history has been linked to seismic phenomena as shown in the codices of pre-conquest civilizations.

However, concerning the earthquakes in Mexico prior to the twentieth century seismic data is negligible.

On July 28, 1957 was recorded in Mexico City, a quake of magnitude 7.7 with its epicenter was located off the coast of Guerrero, reached the intensity of X on the Mercalli scale. He is remembered as "the earthquake Angel" because of the movement because this statue that crowns the Independence Column fell. The total amount of this earthquake was 52 killed, 569 injured, more than 100 landslides and material losses estimated at 100 million dollars at the time.

But the earthquake of September 19, 1985, was the most deadly and destructive it is registered in the history of the city of Mexico.The epicenter was located off the coast of Michoacan, Guerrero, break the contact between the Cocos plate and North America, in an area of ​​50 km x 170 km and about 18 km depth. Its magnitude was 8.1, according to the Institute of Geophysics of the UNAM, lasting nearly four minutes, of which, one minute and thirty seconds correspond to the period of greatest movement.

The intensity at the surface directly above the rupture zone, reached IX on the Modified Mercalli (Considerable damage to buildings suitable scale structures with well designed armor lose the vertical;. Great in substantial buildings with partial collapse damage buildings move the foundation. visible cracks in the floor. broken underground pipes). Despite the long focal length (370 Km) which strongly attenuates the waves on rock site effects in the city's amplified dramatically, especially in certain narrow ranges of frequency of vibration. Because of the deep stratigraphy of the Valley of Mexico, waves that came here to the rocky top surface were compared with tremors elsewhere, an exceptionally high content of energy in a frequency range covering precisely those most amplified clays valley.

In turn, constructs, to experience large swings, vibrating naturally in this frequency range (generally buildings of 7-15 storeys) suffered the greatest damage.

That morning, a tragic wake left behind: dead, wounded, missing, homeless, public and private buildings and residential houses destroyed; property in danger of falling; interruption in water service, electricity and telephone; Water and gas leaks; multiple breaks in the asphalt and gridlock in transit service.

Everywhere arose rescue brigades who selflessly volunteered more than his bare hands. It grew every moment of uncertainty and then despair, no spikes, no shovels, sledgehammers or much less machinery or special equipment for rescue work; Hospitals and ambulances were given no supply, while the shortage of medicines and blood had resulted in the loss of many lives that could be saved.

The Secretary of Defense announced minutes after the quake that the Mexican Army was put into operation the DN-III Plan assistance to the civilian population. For millions of the capital, between 7:19 and 7:22 it was over to begin dramatically.

Appear then the first responses to misfortune: generosity and international support overflows. The president of Cuba, Fidel Castro,

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