recent study has revealed that a series of small, shallow earthquakes in Mexico City in 2019 and 2023 caused unexpectedly strong ground shaking, raising concerns about the impact of future moderate-sized quakes on the city’s buildings. The findings, published in the Bulletin of the Seismological Society of America, suggest that even moderate tremors could cause significant damage, depending on the region’s underlying geology.
Researchers Miguel Jaimes and Gerardo Suárez from Universidad Nacional Autónoma de México analyzed potential damage scenarios for three key areas within the Mexico City basin, modeling earthquakes up to magnitude 5.5. Their simulations were based on past seismic events, including a 2023 quake in La Magdalena Contreras, the 2018 San Juan de Aragón earthquake, and earlier tremors in Milpa Alta and Juchitepec.
The results showed that damage varied significantly depending on location. The soft lakebed sediments in the Juan de Aragón zone amplified shaking, leading to damage in 15% of one- to two-story buildings. The transition zone of La Magdalena saw slightly less impact, with 13% of buildings affected, while the highlands of Milpa Alta experienced only 5% damage.
“We were somewhat surprised that the geographic effect was so dependent on the geotechnical characteristics of each region,” said Suárez. He noted that earthquakes in the transition zone between the lakebed and the highlands pose a very different risk compared to those occurring directly in the lake region.
Mexico City has long been vulnerable to seismic activity, experiencing both shallow local earthquakes and powerful subduction-zone quakes. However, recent small quakes have produced peak ground accelerations even greater than those recorded during the devastating 1985 (M8.1) and 2017 (M7.1) earthquakes.
The study highlights the critical need for urban planners and engineers to reassess seismic risks in Mexico City, not just from large offshore earthquakes but also from local, shallow tremors. “The lesson is clear,” Suárez emphasized. “We must consider that even moderate earthquakes can cause substantial damage, especially in vulnerable areas.”