Mexico earthquake, 2017- Forensic analysis

The UN Global Assessment Report on Disaster Risk Reduction (GAR 2024) report presents 10 case studies, each one with a forensic risk analysis, which systematically examines and investigates the disasters to understand their causes and impacts, as well as the effectiveness of any mitigation measures.

Step 1: Understanding the disaster DNA

What happened?

On September 19, 2017, in the middle of the day, an intraplate earthquake happened about 120 km from Mexico City at a depth of 57 km. Intraplate earthquakes are less common than other types but have occurred in Mexico City since the 1970s. One feature of these earthquakes is that the trembling intensifies as the seismic waves propagate further from the epicentre.

The earthquake, with a magnitude of 7.1, toppled dozens of buildings and damaged hundreds more. At least 326 people died, including 187 in Mexico City. Thousands of volunteers helped rescue workers day and night, using buckets, shopping trolleys, and wheelbarrows to shift tonnes of debris in the search for survivors.

The earthquake showed how effective regulation and other measures can significantly reduce the levels of death and destruction, however. The 2017 mortality rate was significantly lower than for a 1985 earthquake which killed somewhere between 10,000 and 30,000 people. The economic damage was also less severe. While the 1985 earthquake caused damage worth $4.103 billion today (2.7 percent of GDP), losses from the 2017 earthquake were valued at $2.476 billion (0.15 percent of GDP).

Exposure: Where was damage concentrated?

The population of Mexico City fluctuated from 8.8 million in 1980 down to 8.2 million in 1990, then back up to 9.2 million in 2020. Many people live in risk-prone areas on the city's outskirts and commute daily to the city centre.

The 2017 earthquake impacted single-family homes more than public infrastructure. Most residential neighbourhoods near the city centre were damaged, affecting working- and middle-class families the most. Many multi-story buildings collapsed, while more than 20,000 homes, schools, and hospitals were damaged.

Most of the buildings that collapsed were built before the 1987 building code. Collapse factors included inadequate structural support such as concrete columns without steel reinforcements, construction on soft soils, and land subsidence linked to intensive aquifer exploitation. Urban design and construction were also contributing factors.

Vulnerability: Who was affected and why?

Despite Mexico City's wealth, around 27.5 percent of its population lives in poverty, with significant income inequality. Many residents work informally, including street vendors and small business owners. These workers often receive low wages and have limited access to formal employment

Insurance to protect against earthquake losses is rare. Mexico City's Ministry of Finance provides earthquake insurance for public buildings, but high housing costs and gentrification prevent the general population from purchasing it.

In Mexico, 34.8 percent of owned homes are in an irregular situation, meaning they lack deeds, are not in the owner's name, or the owner is unknown. In Mexico City, 337,545 homes (23.6 percent of the total) are irregular. Some 83,601 are registered under someone else's name, and 246,283 lack deeds.

Resilience: what factors limited the impacts?

Several factors likely contributed to the lower death toll in 2017, including the quake's occurrence in the middle of the day when many workers were in the city centre. Despite fewer casualties, the economic impact on poor households was considerable, however.

The situation highlights the importance of good governance. Mexico City's building codes, a central aspect of good governance, have improved over time, requiring buildings to be earthquake-resilient. Governance at both national and city levels contribute to societal resilience.

However, the city's growing population increases earthquake vulnerability. Analysing earthquake risks and events is crucial for better physical and social resilience. Good governance ensures the implementation of effective city-wide physical and societal earthquake resilience. It enables Mexico and other countries to prevent earthquakes from becoming disasters.

Mexico City's building code has evolved significantly since its creation in 1920. Seismic design regulations were introduced after the 1957 earthquake, with further requirements added in 1966 and 1976. An earthquake in 1985 led to significant revisions in 1987, 2004 and 2022. When the 2017 earthquake struck, the 2004 code was in effect.

The 1985 earthquake affected buildings on long-period deposits of the lakebed zone. Post-1985, new institutions were created, such as the National Civil Protection System, the National Disaster Prevention Centre and the Seismic Instrumentation and Registration Centre. Regulations and construction standards were updated, information campaigns were launched, and earthquake drills became common practice.

The 2017 earthquake caused more damage to low- and medium-rise buildings than the 1985 earthquake, particularly in the transition zone. Following the 2017 earthquake, Mexico City established the Integrated Risk Management and Civil Protection System and passed the Law on Integrated Risk Management and Civil Protection, which has been updated since.

Effective land-use planning is crucial for minimizing disaster risks. Mexico City must enforce zoning laws and regulations to ensure new developments are constructed in safe areas while protecting existing infrastructure and the environment.

Integrated disaster risk management requires sustained effort. Mexico City should continue conducting thorough risk assessments to detect potential hazards, vulnerabilities, and exposure levels. A collaborative approach is essential, involving local government, science and technology communities, residents, youth, women, businesses, and civil society organizations

Step 2: Future trends

People

• Over the next decade, the population in Mexico City's outskirts is expected to grow by an average 1.1 percent per year.[1] This growth will likely lead to an increase in informal housing construction for the poor, accompanied by unstable or poorly planned infrastructure such as aqueducts and pipelines.
• Following the 2017 earthquake, an insurance scheme was developed between Swiss Re and the Mexico City government. This scheme protects the city government from losses exceeding its own disaster fund for earthquakes with a magnitude of 8.5 or more. The insurance automatically covers homeowners who meet specific requirements, such as having fully paid their property taxes at the time of the event. This creates a strong incentive for tax compliance, boosting the city's revenues. Together, the insurance solution and the additional revenue will help Mexico City reduce the protection gap associated with major earthquakes. However, informal settlements are not covered by this scheme.

Planet

• Construction in hillside areas without proper risk control and environmental permits could lead to landslides during earthquakes.
• Excessive groundwater extraction in informal settlements jeopardizes the safety of the land where these homes are built.
• In addition to the seismic risk, rapid urban growth is draining groundwater more quickly than it can be replenished. The depletion of subterranean aquifers causes subsidence and massive sinkholes in the city's eastern boroughs such as Iztapalapa, Xochimilco and Tlahuac. Hundreds of houses in these boroughs were damaged on September 19, 2017, when the porous soil under them shifted. With a warming planet, the overuse of water resources will likely increase.

Prosperity

• Approximately 2.5 million workers in Mexico City reside in informal settlements within high seismic risk zones. This situation could significantly impact the city's economy, as these workers represent around 47 percent of the total workforce in Mexico City.

Considering the economic losses related to internal displacement of the employed population of internally displaced persons, Mexico lost an estimated $160 million in economic production due to the September 2017 earthquake.

Step 3: Forensic learning

This section aims to encourage dialogue around the forensic analysis to foster improved decision making. The areas for consideration below are envisaged as an input to stimulate in-country discussion and action plan on future disaster prevention and enhanced disaster risk management.