1985 Mexico City earthquake

. Much of Mexico's volcanic and seismic activity stems from the movement of the North American plate against the Cocos and Pacific plates and it is one of the most active trenches in the world. while Spanish colonial rulers later drained the lakes in a massive hydraulic project (known as the Desagüe) in response to major periodic flooding. The near surface geology of this area is classified into three sections: the old lake bed which is soft clay from volcanic ash with a high water content, a piedmont area, much of which is capped by 5 to 30 meters of lava less than 2,500 years old, and an old river delta area. Mexico City's downtown area mostly lies on the silt and volcanic clay sediments of the bed of the historic Lake Texcoco, which are between seven and thirty-seven meters deep and have a high water content. Above this is a layer of sand and above this is a layer of sand and rock. The western and northwestern parts of the city are outside the old lakeshores and are located on sands from eroding volcanic cones that surround the Valley of Mexico. The southern part of the city rests on hardened basalt lava flows. The old lakebed, with its high water content, is easily moved or compressed. The old lakeshore area also has a fairly high water content, allowing movement, though not as much as the lakebed. The old lava flows have little water content or movement in comparison and are therefore more stable. This resonance amplifies the effects of the shock waves coming from an earthquake far away. However, only certain types of structures are vulnerable to this resonance effect. Taller buildings have their own frequencies of vibration. Those that are six to fifteen stories tall also vibrate at the 2.5-second cycle, making them act like tuning forks in the event of an earthquake. The low-frequency waves of an earthquake are amplified by the mud of the lakebed, which in turn, is amplified by the building itself. This causes these buildings to shake more violently than the earthquake proper as the earthquake progresses. Many of the older colonial buildings have survived hundreds of years on the lakebed simply because they are not tall enough to be affected by the resonance effect. ==Earthquake==

The earthquake occurred in the Pacific Ocean, off the coast of the Mexican state of Michoacán, a distance of more than from the city, in the Cocos plate subduction zone, specifically in a section of the fault line known as the Michoacán seismic gap. The Cocos plate pushes against and slides under the North American plate, primarily along the coasts of the states of Michoacán and Guerrero in Mexico. Volatile trenches along the Cocos plate generally have had seismic events every 30 to 70 years before 1985. However, this particular section of the subduction zone had not had an event for a much longer time. The 19 September quake was a multiple event with two epicenters and the second movement occurring 26 seconds after the first. Because of multiple breaks in the fault line, the event was of long duration. Ground shaking lasted more than five minutes in places along the coast and parts of Mexico City shook for three minutes, The energy released during the main event was equivalent to approximately 1,114 nuclear weapons exploding. The earthquake was felt over 825,000 square kilometers, as far away as Los Angeles and Houston in the United States. In the port of Lázaro Cárdenas, near the epicenter, the 19 September event registered as IX on the Modified Mercalli intensity scale; in parts of Mexico City, it registered the same, even at a distance of about 400 km (249 mi) away. There was no historic record of such a strong quake in Mexico. ==Damage==

Most of the earthquake damage was to buildings. Two reasons are the resonance in the lakebed sediments and the long duration of the shaking. A survey by the government of the damage done found that few buildings from one to five stories suffered serious damage; the same was true for buildings over fifteen stories. When the buildings were built seemed to have an effect as well. Before the 1957 earthquake, there were no building codes with respect to earthquake resistance. Some regulations were passed in that year and more in 1976 after another, stronger earthquake shook the city. However, none of these regulations had an event like 1985's in mind when passed. Most of the seriously damaged buildings were built between 1957 and 1976, when the city was starting to build upwards, in the six-to-fifteen floor range. In second place were buildings from before 1957, possibly because they were weakened by the earlier earthquakes. Structures built between 1976 and 1985 suffered the least damage. At the time of the earthquake, Mexico City had one of the most stringent building codes, based on experience gained from earthquakes in 1957 and 1979. However, the codes were not designed for seismic activity of the intensity experienced in 1985. The damage area corresponds to the western part of the lake zone within of the Alameda Central. Nearly all the buildings that collapsed were located in this lake zone that extended from Tlatelolco in the north to Viaducto Miguel Alemán in the south, Chapultepec Park in the west and to a short distance east of the Zócalo or main plaza. Damage was localized to the center parts of the city, leaving much of the residential outer rim unscathed, but the damage in the affected area was extensive. Over 720,000 tons of debris was removed during the first six weeks after the event. The "Torre de Hospitalización" was built in 1970 with the main building being twelve stories tall. It had two wings, one facing north and the other south, with an inpatient capacity of 536 beds. At the top was a helipad. It was also surrounded by a number of other buildings belonging to the hospital complex such as a blood bank, teaching facilities, offices as well as the original convent. At the time of the earthquake, the hospital was 80% full, and it was shift change time for nurses, doctors and residents. Within minutes, the steel-frame structure collapsed, crushing and trapping many people inside. The infants were found seven days after the initial event and came to be known as the "Miracle Babies" or the "Miracle of Hospital Juárez", having survived without nourishment, water, warmth or human contact during that time. "Topeka" was one of three buildings that collapsed on this block. The magazine Proceso reported that by the time rescue workers reached the building, the owners were already in a hurry to demolish it, without trying to rescue or recover the workers trapped inside. About 150 bodies of workers had already been pulled from the wreckage by fellow employees using their bare hands. All that remains of the factory is a small empty lot with a bronze statue of a woman sewing. Apartments were built on the remainder of the property. In this school the classes normally started at 7 o'clock in the morning, so the students were already in class. Some data indicate that around 120 people died and some disappeared in this building. The building was split in two by the earthquake; the part that overlooked Humboldt Street remained standing while the part that overlooked Iturbide Street fell down completely. The Iturbide wing collapsed floor to floor and the debris tumbled into the street. Central Communications Center On Eje Central and Xola Avenue, at the southern end of the lake-bed zone was (and is) the Secretaría de Comunicaciones y Transportes (Ministry of Communication and Transportation), a reinforced concrete structure with its microwave tower. This structure failed, causing the near total collapse of long-distance communications between Mexico City and the rest of the world. The area is now a market. It was located at the corner of Balderas and Avenida Juárez in the historic center and completely collapsed within moments of the quake. Apartment complexes in Tlatelolco There were two apartment complexes in the area of the city called Tlatelolco to the north of the historic center that became major scenes of disaster, the Conjunto Urbano Nonoalco Tlatelolco and the "Multifamiliar Juárez" near the Metro Centro Médico. Together, these apartment complexes were a large percentage of the 30,000 units lost, with the city losing about 30% of its living space. covering an area of about . It had 102 buildings with seven medical facilities, twenty-two schools and about 500 small businesses, serving the 80,000 people who lived there. Constructed under the presidency of Adolfo López Mateos, it was considered the most important complex of its kind in the country. In the Conjunto Urbano, two of the three modules of the building called "Nuevo León", at thirteen stories tall, completely collapsed, while the other one was severely damaged. In other buildings, dozens of people terrified by the event jumped from high windows to their deaths, trying to escape. Buildings A1, B2 and C3 of the Multifamiliar Juárez complex partially collapsed with a total of nine structures eventually being demolished. The last image broadcast from the studio was that of Lourdes Guerrero stating "... it's still shaking a little (sigue temblando un poquitito), but we must take it calmly. We will wait just a second so we can keep talking." 1,687 school buildings were damaged. Interruption of classes, either to the lack of facilities and/or the need to help with rescue efforts, affected over 1.5 million students. Mexico City Metro On the day of the quake, the Metro stopped service and completely shut down for fear of electrocution. This caused people to get out of the tunnels from wherever they were and onto the street to try to get where they were going. At the time, the Metro had 101 stations, of which 32 were closed to the public in the weeks after the event. On Line 1, there was no service in stations Merced, Pino Suárez, Isabel la Católica, Salto del Agua, Balderas or Cuauhtémoc. On Line 2, there was no service between stations Bellas Artes and Taxqueña. On Line 3 only Juárez and Balderas were closed. Line 4 continued to operate normally. All of the closed stations were in the historic center area, with the exception of the stations of Line 2 south of Pino Suárez. These Line 2 stations were located above ground and were closed was not due to damage to the Metro proper, but because of surface rescue work and clearing of debris. ==Death toll==

To this day, the death toll has been in dispute. About 5,000 bodies were recovered from the debris and represent the total of legally certified deaths but does not include those who were missing and never recovered. The main reason that the figures have been disputed is the government's response to the tragedy. President Miguel de la Madrid ordered a news blackout and did not address the situation at all for 39 hours after the event. When the government did give estimates of the number killed, they ranged from 7,000 to 35,000. Consequently, most of the populace believes that the true numbers have never been revealed. According to government figures, approximately 250,000 people lost their homes directly due to the earthquake. Unofficial sources put that figure much higher. Some sources say that more than 50,000 families lost their homes. INEGI reports that 700,000 people in Mexico City and the suburbs in the State of Mexico lost their homes. ==Response==

In the hours and days immediately after the first shock, there was an enormous response and solidarity among the city population of 18 million people. Ordinary citizens organized brigades to help with rescue efforts and to provide food, clothing and emotional support to the homeless. as well as rescue, sanitary efforts and other, with 1,836 soldiers initially sent in and another 1,500 conscripts sent later. At many levels of the government, who was helped and by how much was determined by one's standing vis-à-vis the PRI. Those belonging to the party received preference and those considered opposition received the runaround. President de la Madrid refused to cut foreign debt payments to use the money to help with the recovery effort. The government's response to the earthquake was widely criticized at various levels of Mexican society, being seen as both authoritarian and incompetent. Few countries sent rescue delegations to support these efforts. ==Political consequences==

At the time of the earthquake, Mexico was in its fourth year of a foreign debt crisis, and a contracting economy causing serious political problems for the Institutional Revolutionary Party (PRI). Much of the PRI's authoritarian nature was tolerated because the country had seen four decades of economic expansion of six percent or better. When this disappeared, the PRI's power base began to shrink. Its reputation was damaged further when the government seemed to be deliberately downplaying the number of earthquake victims. President de la Madrid made relatively few public appearances afterwards and during those he did, he received strong heckling, in contrast to the near-reverence that past presidents enjoyed at such events. The severe damage in so many buildings, including in many public works construction projects to house the rapidly growing population of Mexico City, was blamed on lax enforcement of building codes. Critics argued that the lack of enforcement of such codes was indicative of corrupt practices in all levels of government. The stepping-in of non-PRI organizations to take over where the government could not, also took its toll on PRI's reputation. Burton Kirkwood stated, "Out of the disaster emerged the realization that a viable civil society existed in Mexico. This revelation also caused many to consider why they needed a centralized state that so obviously could not care for its people. As a consequence, the opposition movements pointed to the government's shortcomings and advanced candidates for the greater goal of defeating the PRI." Shortly after the event, the PRI began to face serious challenges at the polls, resulting in attempts to rig elections. ==Legacy==

, located adjacent to the Alameda Central, a monument was made honoring the victims and rescuers of the earthquake.|thumb One preparation that was made for any future events was the alert system, Sistema de Alerta Sísmica (SAS), which sends early-warning messages electronically from sensors along the coastal subduction zone in Guerrero. It was expanded to a similar area on the coast of Oaxaca. An alarm is supposed to go off in Mexico City (similar to an air-raid siren) when an earthquake of 6.0 or higher is detected. Affiliated with the Civil Protection Committee is the "Brigada de Topos de Tlatelolco" (Mole Brigade of Tlatelolco). This group arose from youths who spontaneously volunteered to risk their lives crawling into collapsed buildings to look for survivors. Despite having no equipment, training or knowledge of rescue tactics, Despite warnings and predictions, in 2005, an estimated 32 million people lived in the high-risk lakebed area. In 2005, there were still two camps where approximately eighty families are waiting for relocation from the earthquake. Centuries-old structures have been reinforced across the city and new construction must comply with very strict codes. There are several instances of tall buildings in Mexico City incorporating earthquake-resistant engineering. A few notable examples are: the Torre Latinoamericana, one of the first buildings in Mexico City to do so, the Torre Ejecutiva Pemex, built before the 1985 earthquake, and the Torre Mayor, built in 2003. Every 19 September, in all public buildings at Mexico City and all the nation the civil protection authorities conduct evacuation drills to evaluate the evacuation response in the case of an earthquake. On 19 September 2017, 32 years after the 1985 earthquake, Mexico City also faced another earthquake at around 13:14 CDT (18:14 UTC), nearly two hours after the earthquake drills took place and on 19 September 2022, 37 years after the 1985 earthquake and 5 after the 2017 one, the 2022 Michoacán earthquake struck Mexico at 13:05 CDT (18:05 UTC). File:Ceremonia 30 años del Terremoto de México de 1985 - Plaza de la Solidaridad 01.JPG|Mayor Miguel Ángel Mancera presides over a minute of silence for the earthquake victims at the 30-year commemoration File:Statue of Placido Domingo in Mexico City.jpg|A statue in Mexico City to Plácido Domingo as a recognition to his contributions to 1985 Mexico City earthquake victims and his artistic works. ==See also==