The Earthquake That Changed Mexico
Shortly before midnight on September 29th, 2015, the residents of Mexico City woke up to a loudspeaker blaring. The announcement “Alerta Sismica. Alerta Sismica.” repeated for roughly 30 seconds, accompanied by what sounded like the world’s worst fire drill. There was no escape from the deafening noise.
A M4.6 earthquake near Ometepec, Guerrero triggered the earthquake alarm. Over 350km away from the Guerrero Coast, in the heart of Mexico City, trees and lampposts swayed. Yet, for most Mexico City residents, the earthquake passed unnoticed. The seismic alarm seemed almost like a practice drill.
Built on a former lakebed, Mexico City is vulnerable to many natural disasters. The city faces floods and ash falls from the nearby Popocatepetl volcano. The most devastating natural disaster in recent Mexico City history took place on September 19th, 1985, irrevocably changing the city, the government of Mexico, and an entire scientific discipline in the process.
Last month, Mexico City commemorated the 30-year anniversary of the September 19th, 1985 earthquake. Nearly 200 of the world’s brightest earthquake scientists and students met September 16-19, 2015 for a conference in the city. Attendees included Hiroo Kanamori, Raul Madariaga, Eduardo Miranda, Robert Clayton, Francisco Sanchez-Sesma, Carlos Mendoza, and Kojiro Irikura, along with dozens of students and earthquake scientists. Participants discussed the changes to earthquake science as a result of the 1985 M8.1 earthquake.
What Happened on September 19th, 1985?
The morning of September 19th, 1985 was like any other Thursday. Children waited in classrooms. Adults sipped their morning coffee. Families ate breakfast. The city's professionals raced through traffic to work.
And then it happened.
At 7:17 in the morning, a powerful earthquake struck Mexico’s Michoacán coast. According to the United States Geological Survey (USGS), the shaking toppled 412 buildings in Mexico City. Mexico’s earthquake was international news and a national disaster.
According to the Mexican National Defense Secretary’s records, there were approximately 2,000 casualties. In stark contrast to those numbers, the USGS estimates least 9,500 casualties. Other estimates are much higher, including that provided by Mexico’s National Seismic Service. They place the number of casualties closer to 40,000.
As a result of the earthquake, the government's corruption and poor enforcement of building codes was thrown under the spotlight. Slow government response to the disaster and underreported death tolls may have been the last straw. The earthquake is often cited as toppling the 71-year dictatorship that ruled Mexico.
The Michoacán earthquake which struck Mexico that September morning is known in the capital as the “earthquake of 1985”. It was the largest Mexican earthquake in recent memory. The event was so destructive that 3,124 buildings were severely damaged in Mexico City, besides the buildings that collapsed. Nearly 100,000 more buildings needed repair and retrofitting after the quake. An estimated 250,000 of the city’s residents became homeless in an instant.
Outside of the city, damages occurred as well. According to the USGS, “about 60 percent of the buildings were destroyed at Ciudad Guzman, Jalisco. Damage also occurred in the states of Colima, Guerrero, Mexico, Michoacán, Morelos, parts of Veracruz and in other areas of Jalisco.”
Landslides occurred in at least two other Mexican states. Soil liquefaction took place near the epicenter of the quake. On the Pacific Coast of Mexico, a tsunami of up to 3 meters struck. Swimming pools rocked in response to the quake as far away as Smithsburg, Maryland. More than 20 million people felt the initial tremor. Individuals in Guatemala City, Guatemala and Houston, Texas reported feeling it.
Mexico City produces the bulk of the nation's GDP, and nearly 1/3 of the population of Mexico lives within the metropolitan area. The vast majority of casualties and damages happened in the Valley of Mexico. Despite the effects observed outside of the capital, this was Mexico City's disaster.
Dr. Xyoli Perez Campos, the head of Mexico’s National Seismic Service (Servicio Sismológico Nacional), commented at the conference that Mexico City has only “two generations – those who lived through the 1985 earthquake, and the young people who did not.”
Towards a Greater Understanding of Earthquake Science
Despite the extent of the damage and casualties, this disaster had a net positive impact on society. Mexico formed partnerships with Japan and the United States as a consequence of the earthquake. Exchange programs brought Mexican students to Japan to study earthquake engineering and related disciplines. Many Mexican students also began to study earthquake sciences in the United States and France. Mexico’s Sistema Nacional de Protección Civil (National System of Civil Protection) formed in 1986.
The Mexican National University’s (UNAM) Institute of Engineering reinvigorated its focus on earthquake engineering. At the time of the quake, the institute was relatively new. At UNAM, students who would one day leave a major mark on the global understanding of earthquake science studied. Some, like Prof. Eduardo Miranda of Stanford University, were sitting in the university’s classrooms when the 1985 earthquake struck.
Prof. Miranda's work continues to make a major impact on the understanding of soil-structure interaction and site effects. He credits many of his own scientific contributions to the differences he noticed between what he was learning in the classroom with what he lived through in 1985.
Earthquake science in the early 1980s was largely qualitative. The ability to use real-time data from earthquakes gathered at multiple stations was limited. Instrumentation in general was just beginning to take off and GPS monitoring was only an idea. As a result, building codes were little more than best-guess estimates.
According to Miranda, the intensity of the Mexico City 1985 earthquake was 4x higher than the code engineers designed for. Sites only 600 meters apart exhibited obvious differences when a series of earthquakes struck the city in May 1962. Mexico's seismicity became popular in earthquake science circles thanks to the site effects and damage caused by the 1985 rupture sequence and the shear amount of data available for the events.
According to Caltech Prof. Hiroo Kanamori, “the most important aspect [of the 1985 Mexico City earthquake] was that a large earthquake some 350 km away can affect large (and small) structures significantly depending on how the energy travels and gets coupled into the ground... As a result, the site amplification was very significant. Thus, detailed studies on the structure not only beneath Mexico City but also along the entire path are important.”
Kanamori also emphasized the importance for early warning systems and earthquake preparedness. These factors could have saved many lives in 1985, and save many today.
The 1985 Mexico City earthquake made a lasting impact on earthquake science in many ways. As Prof. Carlos Mendoza, formerly of the USGS and currently a professor at UNAM’s Juriquilla campus, stated in a recent interview:
“There is no doubt that the 1985 earthquake contributed greatly to our understanding of how earthquakes work. It was one of several large earthquakes in the 1980s that prompted the study of earthquakes with strong-motion data from up to the moment, as well as source studies, the use of asperities in sources, etc… This earthquake was notable because it could be studied right after the event. There were quantified effects.”
Mendoza was an intern at the USGS in 1985 and speaks both Spanish and English. He recalls answering phones at the USGS for 2-3 days following the earthquake. "I didn’t know anyone in Mexico City at the time, [but] I could get a feel for what had happened. As a result of the earthquake, much of the work I did centered around Mexico.”
On a local level, the earthquake led to the development of more strict norms for new buildings. According to Sanchez, “These changes influenced the professional practice and were adopted in some rules of construction in other federal entities. They also generated stricter requirements for the participation of accredited professionals [in construction] in order to assign responsibilities for future damages and to guarantee that structures and installations of major importance, particularly in important structures (such as schools, hospitals, communications centers, etc.) could continue operating even during urban emergencies.”
Attendees at the 30th Anniversary commemorative conference viewed a photo exhibit in the poster hall. Titled “Riesgo Social”, the exhibit showed unsafe structures and building practices around Mexico City.
Despite significant changes to Mexican building codes, many structures are poorly positioned or built. Unofficial and unsanctioned construction is a chronic problem in Mexico City. Several of the most vulnerable zones in the city include deep gullies and trenches. In and along these gullies, people build makeshift homes and small businesses. It's not uncommon to see structures built on the edge of steep drops or precipices in the city. In the event of an earthquake, they’re vulnerable to mudslides, rockfalls, or structural collapse.
Homes and apartment buildings around Mexico City frequently have what Mexicans call “piso blando”. In English, these are "soft-story buildings." They don’t include the necessary shear walls and support columns to remain stable in an earthquake. As a result, they are prone to collapse under seismic stress.
Without the proper divulgation of earthquake engineering, people cut corners. They remove support walls to make room for kitchen islands or to change a closed floorplan to an open one. They dilute materials like concrete below the necessary strength. In order to meet the homeowner or building owner’s budget, or as a result of worker theft, they use substandard materials. The population is largely unaware of what defines a stable, safe structure. Most residents either can’t afford or don’t see the need to hire structural engineers.
Although the Riesgo Social photo project aims to communicate this message, it wasn’t open to the people who need it most - the public. It was shown in a three-day conference to a select group of individuals who are already aware of the problem. The message, powerful as it is, never made it to the people.
Societal and Scientific Norms
Roberto Eibenschutz is a prominent urban planner in Mexico City, and he is concerned about the types of construction he sees. During the conference, Eibenschutz expressed particular concern about Mexico City’s new airport. The airport is being built on very soft soils, with runways stretching over 5 kilometers. Eibenschutz has reason to be vocal. He assisted in the re-cementation of the Nuevo Leon building in 1982. The building's collapse was one of the most infamous disasters of the 1985 earthquake.
The Tlatelolco complex where the Nuevo Leon building stood was a novel concept when it was built. The complex offered several tall, thin apartment buildings and housed over 80,000 people. Residents and inspectors noticed damage to the Nuevo Leon building in 1981. In 1982, it was repaired to meet the standards of the era.
The Nuevo Leon building collapse killed hundreds. The building became a symbol of solidarity during the cleanup period after the earthquake. Family and community members worked to free their neighbors and relatives from the rubble. Several of Mexico City’s professionals lived or had family in this middle-class apartment building.
In Eibenschutz’s words, the Tlatelolco housing project “was an example of what not to do….Built over unstable soils, the buildings were also poorly designed. The construction exhibited numerous technical failings…they were built quickly, and the urgency to finish the project was also a point of failure.” The buildings were also overpopulated.
Speaking at the conference, Eibenschutz stressed the importance of creating legally-binding codes for construction, not just norms. He also stressed his belief that too much focus is placed on rescue, and prevention is often overlooked.
In Eibenschutz’s words, “As an urban planner, the 1985 earthquake gave me a very clear understanding of the importance that should be given to location and vulnerability analysis when we are in the process of decision taking for big investments or for new areas of urban development. Too much importance has been given to the cost of land and infrastructure, leaving behind the evaluation of risk and vulnerability. It is very important to be conscious that you may improve the design of buildings, but you cannot improve location conditions.”
In talks at the same conference, Dr. Jorge Aguirre of UNAM’s Institute of Engineering and Dr. Juan Carlos Mora, a professor of geophysics at UNAM, noted that indifference for safety measures occurs across socioeconomic levels. The seismic alarm is a good example.
Even educated and informed members of the population don’t always heed Mexico City’s seismic alarms. At the end of September, a series of minor tremors struck the city and triggered the earthquake alarm on two separate occasions. Safety protocols mandate that individuals exit their residences and wait on the street or at green and white-labeled reunion points outside of businesses and restaurants when the alarm sounds. Few people paid heed to the alert.
Inside UNAM, the nation’s leading university in geosciences and earthquake engineering, a student commented, “My sandwich is going to take longer, thanks to that alarm.” Indifference isn’t exclusive to the city’s younger generation, either. A professor in UNAM’s Social Work school stated that he didn’t leave his classroom for the alarm because there were people outside that he didn’t like.
Despite limited housing options and growing population stress, Mexico’s government, universities, and scientists have the technical knowledge to save lives and prevent disasters. Around the world, knowledge gained from Mexico City’s M8.1 September 19th, 1985 earthquake is saving lives. Despite significant technological and scientific advances stemming from the 1985 earthquake, the city’s population remains ignorant of (and overly casual about) the seismic hazard of their city.
As Mendoza posited when we spoke, “… the level of preparedness is obviously a lot better and a lot of work has been done since 1985, but the average person has a hard time identifying with what’s going on. False alarms happen. How will people respond in a large earthquake? Have living structures improved? Is the Colonia Roma prepared? How and to what extent have technical advances been incorporated? It’s not just about science. Politics and technical aspects are both important. There’s so much to learn.”
1. Personal communication with Hiroo Kanamori, (date)
2. Interview with Carlos Mendoza, 19 September 2015.
3. Personal communication with Tomas Sanchez (date)
4. Personal communication with Roberto Eibenschutz (date)
5. Conference: “Avances y Retos en Sismologia, Ingenieria, y Gestion de Riesgos a 30 Anos del Sismo de 85”, Mexico City, 17-19 September 2015.