1985 MEXICO CITY EARTHQUAKE

The '1985 Mexico City earthquake' was one of the most devastating earthquakes in the history of the Americas.
On Thursday, September 19, 1985, at 7:19 AM local time, Mexico City was struck by an earthquake of magnitude 8.1 on the Richter scale. The epicentre of the earthquake was off the Pacific coast of the Mexican state of Michoacán, a distance of 350 km, in the Cocos Plate subduction zone.
As a result of the earthquake, according to official government statistics, at least 9,000 people were killed, 30,000 injured, and 100,000 left homeless. 412 buildings were destroyed and over 3,000 seriously damaged.

Contents

The Damage

Death count

Notable victims

The Aftershock

Emergency response

Structural Engineering issues

Economic Effects

Later effects

References

External links

The Damage

Shaking from the quake lasted three to four minutes and was felt over 825,000 square kilometers. The most damaged zones in the city were those in the bed of the historic Lake Texcoco, where the prevailing silt and volcanic clay sediments amplified the shaking. Building damage was worsened by soil liquefaction which causes the loss of foundation support and contributes to dramatic settlement of large buildings. The buildings most damaged were from 6-15 stories in height

Death count

Many residents of Mexico City dispute the official statistics, and believe that deaths from the quake exceeded 60,000 and more likely approached 100,000. Their reason for doubt is that their one-party government (at the time) was infamous for under-playing negative statistics whenever possible.
A precise count of those killed in the two quakes has never been determined, and reported numbers tend to vary widely:

★ 4,200: BBC [1]

★ 4,541: Mexican Government [2]

★ 10,000: Christian Science Monitor [3]

★ 10,000: CNN [4]

One hundred thousand housing units were destroyed, together with many government buildings, schools, parts of the Televisa Chapultepec campus, the famous Cafeteria Superleche restaurant, a trio of 28-story towers "Complejo Pino Suárez", The famous 1900`s Hotel Regis, the Continental Hilton, the two buildings of the Nuevo León section of the Tlatelolco housing development near the Plaza de las Tres Culturas and at least three large hospitals. Between $9-12 billion dollars of damage were caused in just over three minutes.
The quake caused major portions of three of the city's largest hospitals to collapse, burying some 1,200 people. Loss of these hospitals severely limited the city's ability to care for quake-injured patients. Juárez Hospital completely collapsed, and survivors were retrieved from the structure as late as ten days after the earthquake by tunneling through the debris between the floor slabs. [5].

Notable victims

★ Plácido Domingo's aunt, uncle, and two of his cousins were killed in the collapse of the "Nuevo León" building.

★ Rock musician Rodrigo "Rockdrigo" González was killed in the quake.

The Aftershock

There was an additional magnitude 7.5 aftershock 36 hours later (the evening of Friday, September 20), which caused widespread panic among the already battered population of the city. A magnitude of 7.5 is enough to destroy buildings within a radius of 150 kilometers.

Emergency response

A dramatic emergency response was immediately mobilised. Assistance from neighbouring Mexican states and from abroad was received, and was followed by international relief.
Aid came in the form of 296 flights originating from 45 different countries, assistance by land from six nations, and relief in the form of cash donations [6].
Several heads of states traveled to the city, among them the President of Brazil, José Sarney, the President of Venezuela, Jaime Lusinchi, the head of the Spanish government, Felipe González, Alan García, from Peru, and the wife of United States president Ronald Reagan, Nancy, who brought a gift of one million dollars.

Structural Engineering issues

The main causes of building loss included: corner building failure (42%), collapse of intermediate floors (40%), collapse of upper floors (38%), `pounding:' (one building repeatedly striking another during earthquake vibrations) (15%), and foundation failure (13%) [7].
Several notable buildings were relatively untouched by the quake, having been constructed based on codes with earthquake resistant provisions. One such building is the Torre Latinoamericana building in downtown. As a consequence, earthquake survivability has been an issue of serious consideration ever since. When Torre Mayor was built in 1999, numerous safety mechanisms, including dramatic internal truss structures, were included to assure safety in the event of another major tremor. Torre Mayor was built to survive an 8.5+ magnitude earthquake.

Economic Effects

The quake is still well-remembered by most city residents today, as it led not only to massive structural damage and human loss, but also to the complete failure of many under-insured businesses in a mostly informal economy. Countless people whose livelihood was lost in the quake left the city, and many even left the country, seeking work in the other countries.

Later effects

In an effort to be better prepared for future devastating earthquakes, the Mexican government funded a state-of-the-art alert system, Sistema de Alerta Sísmica (SAS)^[1] that sends early-warning messages to Mexico City electronically from sensors located along the coastal subduction zone in Guerrero. A similar system is being built in Oaxaca^[2] to the south. In the event that seismic activity is detected, warning sirens will sound, giving city residents up to a minute's warning that a quake is coming.
The last considerable earthquake in Mexico City had a magnitude of 7.4 on the Richter scale, on September 30, 1999 at 11:27 am. Only one death was reported, caused by a falling pipe. Many buildings were damaged.

References

1. http://www.cires.org.mx/
2. http://www.cires.org.mx/saso_es.php

External links

★ Images from the earthquake aftermath

★ Image album from the Mexican National Seismology Service at UNAM