A new study has revealed that moderate earthquakes in Mexico City could cause significant damage to buildings, depending on the region’s underlying geology. The findings, published in the Bulletin of the Seismological Society of America by Miguel Jaimes and Gerardo Suárez of Universidad Nacional Autónoma de México, highlight the risks posed by local seismic activity beyond the well-known large subduction earthquakes.
Mexico City has recently experienced swarms of small, shallow earthquakes, particularly in 2019 and 2023, which generated unexpectedly strong ground shaking. These events prompted researchers to investigate how shaking from a moderate earthquake with a magnitude up to 5.5 might impact buildings across different parts of the city.
Geology MattersDamage Varies by Region
The study modeled earthquakes in three key locations, based on past seismic events:
- Juan de Aragón (lake zone, 2018 earthquake site). La Magdalena Contreras (transition zone, 2023 earthquake site). Milpa Alta highlands (historical earthquakes in 1985 and 1995)
The results were striking:
- A Juan de Aragón earthquake would damage 15% of one- to two-story buildings, due to the soft, supersaturated lakebed sediments amplifying seismic waves.
- A La Magdalena earthquake would damage 13% of these buildings, as it lies in the transition zone between the lake and hills.
- A Milpa Alta earthquake would damage only 5%, as the harder, more stable geology of the highlands absorbs seismic energy more effectively.
“We were somewhat surprised that the geographic effect was so dependent on the geotechnical region,” said Suárez. “The potential damage is very different between the lakebed and the transition zone compared to the highlands.”
Microearthquakes and the Unexpected Strength of Ground Shaking
Historically, Mexico City has suffered devastating earthquakes, such as the magnitude 8.1 earthquake in 1985 and the magnitude 7.1 earthquake in 2017. However, recent microearthquakes have revealed surprising new data.
“The large ground accelerations recorded during recent small earthquakes were greater than those recorded in 1985 and 2017,” Suárez explained. This unexpected intensity was captured by improved seismic instrumentation, which has become more widespread and sensitive in recent years.
The study also found that one- to two-story buildings were particularly vulnerable because the high-frequency seismic waves of local earthquakes match their natural vibration frequency. Suárez compared this resonance effect to pushing a child on a swing in sync with its movement, amplifying the impact.
The research underscores the need for urban planners and earthquake engineers to reassess seismic risk in Mexico City. While much attention has been given to large subduction earthquakes, local crustal faults though less frequent can also cause substantial damage.
“The lesson is clear,” Suárez emphasized. “Mexico City’s seismic risk comes not only from large and frequent subduction earthquakes but also from local crustal sources, which can be highly damaging in specific regions.”
With Mexico City’s dense population and varied geology, preparedness measures including building reinforcements and updated seismic regulations will be critical to mitigating future risks.