A new study has highlighted the surprising strength of ground shaking caused by recent shallow earthquakes in Mexico City, raising concerns about the potential impact of moderate seismic events on the city’s buildings. Researchers Miguel Jaimes and Gerardo Suárez from Universidad Nacional Autónoma de México (UNAM) have modeled earthquake scenarios to assess possible damage emphasizing the role of local geology in amplifying shaking.
Published in the Bulletin of the Seismological Society of America, the study analyzed three regions based on past seismic activity: La Magdalena Contreras (2023), San Juan de Aragón (2018), and the Milpa Alta and Juchitepec earthquakes (1995 and 1985, respectively). Their findings suggest that even moderate earthquakes, up to magnitude 5.5, could cause significant structural damage in certain areas.
The researchers found that ground shaking in the lakebed zone of San Juan de Aragón would damage about 15% of one- to two-story buildings due to the area’s soft, saturated sediments. In contrast, similar earthquakes in La Magdalena’s transition zone situated between the lakebed and hill areas would damage 13% of such structures. Meanwhile, an earthquake in the Milpa Alta highlands to the southeast would lead to about 5% damage.
Suárez noted “We were somewhat surprised that the geographic effect was very dependent on the type of geotechnical region the earthquake occurred, potential damage is very different for earthquakes in the transition zone between the old lakebed and the highlands than in the lake region.”
Mexico City has long been vulnerable to seismic activity, feeling the effects of both deep subduction-zone earthquakes and shallow, local crustal tremors. The study underscores that local earthquakes though often overlooked could pose serious risks. Advanced seismic monitoring in recent years has captured microearthquakes that produce peak ground accelerations exceeding those of Mexico City’s most devastating tremors, including the 1985 (M8.1) and 2017 (M7.1) earthquakes.
The research suggests that local, moderate earthquakes could have a disproportionately large impact on shorter structures, particularly one- to two-story buildings. This is due to the high-frequency seismic waves, which resonate with these buildings’ natural vibration periods akin to pushing a child on a swing at just the right rhythm to amplify motion.
Suárez emphasized that Mexico City’s earthquake risk is not limited to large subduction events but also includes local crustal quakes, which, though less frequent, can still cause substantial damage. The findings serve as a call to action for urban planners and engineers to integrate these risks into future seismic preparedness and construction policies.