1985 Mexico City Earthquake: Collapse, Rescue and Reform

The 1985 Mexico City earthquake struck at 7:17 a.m. on 19 September 1985, when a magnitude 8.0 earthquake off the Pacific coast shook central Mexico. Although the epicentre was more than 350 kilometres away, soft lakebed soils amplified the shaking in Mexico City, bringing down hundreds of buildings and killing thousands of people. The slow official response and the vast volunteer rescue effort that filled the gap left deep marks on Mexican politics and society.

Background: a city on a lake

Mexico lies above the boundary where the Cocos Plate sinks beneath the North American Plate along the Pacific coast, producing frequent large earthquakes. The 1985 earthquake ruptured a section of this subduction zone off the state of Michoacán, sometimes called the Michoacán gap because it had not produced a great earthquake for decades.

Mexico City itself is built largely on the bed of Lake Texcoco, which the Aztec capital Tenochtitlan once occupied and which was drained over the following centuries. The old lake sediments are soft, water-saturated clay. Engineers already knew that this ground amplified seismic waves, but the scale of the effect in 1985 surprised them.

The capital had been damaged by distant earthquakes before. In 1957 a magnitude 7.7 earthquake off the coast of Guerrero toppled the golden Angel of Independence statue on Paseo de la Reforma and killed dozens of people in the city. Building rules were tightened after 1957, but many of the medium-rise concrete buildings put up during Mexico City’s rapid growth in the 1960s and 1970s were not designed for shaking as long and strong as that of 1985. By then the metropolitan area had grown to roughly 17 to 18 million people, among the largest cities in the world.

The earthquake

The main shock lasted for around two minutes in parts of the capital. In the lakebed zone, the ground shook with a dominant period of about two seconds, which matched the natural period of buildings between about six and fifteen storeys tall. These medium-rise structures resonated, swaying more and more violently, while many lower and taller buildings survived.

Near the coast, in Michoacán, Guerrero and Jalisco, the earthquake damaged towns and ports such as Lázaro Cárdenas and Ciudad Guzmán, but these areas suffered far fewer deaths than the capital. In Mexico City, telephone lines and electricity failed, cutting the city off from the rest of the world for hours, and the first news reached many foreign countries through amateur radio operators.

Around 400 buildings collapsed completely and thousands more were badly damaged, mainly in the historic centre and neighbouring districts such as Colonia Roma, Doctores, Guerrero and Tlatelolco. On the evening of 20 September a strong aftershock of about magnitude 7.5 caused further damage and panic.

Notable collapses

Some of the worst losses occurred in public buildings. Parts of the Juárez Hospital and the General Hospital collapsed, killing patients and staff. At the Tlatelolco housing complex, a large section of the Nuevo León apartment building fell, killing hundreds of residents. The Televisa broadcasting tower, the Hotel Regis and parts of the Ministry of Communications and Transport were destroyed.

In the garment district around San Antonio Abad, many small factories collapsed with seamstresses inside. Reports that some owners rescued machinery before workers caused public outrage, and surviving seamstresses formed an independent union, the 19 de Septiembre union.

Rescue and response

The government of President Miguel de la Madrid was widely criticised for a slow and confused response. At first it declined foreign assistance, before accepting rescue teams and aid from many countries. Specialist teams with sniffer dogs and listening equipment arrived from countries including France, Switzerland, Spain, Israel and the United States. Official information was limited and death figures were disputed.

Ordinary citizens filled the gap. Thousands of volunteers dug through rubble with their hands, directed traffic and organised food, water and shelter. Volunteers who crawled into collapsed buildings became known as Los Topos (“the moles”) and later formed a permanent rescue organisation. Among the most famous rescues were the newborn babies pulled alive from the ruins of hospitals days after the earthquake, often called the “miracle babies”. The opera singer Plácido Domingo, who lost relatives in the Nuevo León building, joined the rescue efforts at Tlatelolco.

Death toll and damage

The number of deaths has never been settled. Official figures were about 5,000 to 6,000, while most later estimates put the toll at around 10,000, and some survivors’ groups claimed many more. Tens of thousands of people were injured, and tens of thousands of families lost their homes. Damage was estimated at several billion US dollars, a severe blow to an economy already in crisis after the 1982 debt crisis.

Political and social consequences

Historians often see the earthquake as a turning point in Mexican civil society. The capable self-organisation of residents contrasted with the failures of the state and the governing Institutional Revolutionary Party (PRI), which had ruled Mexico since 1929. Neighbourhood associations and survivors’ groups formed to demand housing and accountability, and many later joined wider movements for democratic reform.

A large public housing reconstruction programme rebuilt or repaired tens of thousands of homes in the centre of the city. The disaster is widely seen as one factor behind the growing challenge to PRI rule that became visible in the disputed presidential election of 1988.

Reforms

The government issued emergency building regulations in 1985 and a new Mexico City building code in 1987, with stricter rules for structures on the lakebed. The National Civil Protection System (SINAPROC) was created in 1986, followed by the National Centre for Disaster Prevention (CENAPRED) in 1988. In 1991 the Mexican Seismic Alert System began operating, giving Mexico City residents seconds of warning before shaking arrives from coastal earthquakes.

By coincidence, another powerful earthquake struck central Mexico on 19 September 2017, the anniversary of the 1985 disaster, only hours after the annual earthquake drill. Hundreds died, but the improved codes and alert system are credited with limiting the damage.

Timeline

• 1985, 19 September, 7:17 a.m.: A magnitude 8.0 earthquake strikes off Michoacán, devastating Mexico City.
• 1985, 20 September, evening: A magnitude 7.5 aftershock causes further collapses.
• 1985, late September: Rescuers pull newborn babies alive from collapsed hospitals.
• 1985, October: Emergency building regulations are issued for Mexico City.
• 1986, May: The National Civil Protection System is created.
• 1987: A new Mexico City building code is adopted.
• 1991: The Mexican Seismic Alert System begins operating.
• 2017, 19 September: Another major earthquake strikes on the anniversary.

Legacy

The 1985 earthquake remains part of the collective memory of Mexico City, commemorated every year with drills and ceremonies. For engineers it became a classic case study of site amplification, comparable to the damage on soft ground during the Loma Prieta earthquake in California four years later. It also stands alongside other great twentieth-century urban disasters, such as the Tangshan earthquake in China, as a lesson in how ground conditions and building quality decide who lives and who dies.

Why it matters

The 1985 earthquake revealed the deadly combination of soft ground and vulnerable buildings, and it reshaped earthquake engineering and disaster planning in Mexico. Just as importantly, it showed the strength of citizen action and helped change the relationship between Mexicans and their government.