Every year on September 19, Mexico City pauses to remember two devastating earthquakes: the magnitude 8.0 quake of 1985 and the magnitude 7.1 quake of 2017, both of which struck on this same date decades apart. As the anniversary approaches again, seismologists and civil engineers are once more explaining why the Mexican capital is so uniquely vulnerable to earthquake damage, even when the epicenter lies hundreds of kilometers away along the Pacific coast.
The answer lies beneath the city’s streets. Much of Mexico City was built atop the drained bed of ancient Lake Texcoco, leaving behind soft, water-saturated clay sediments instead of solid bedrock. When seismic waves pass through this loose subsoil, they don’t simply travel through—they get trapped and amplified, causing the ground to sway and vibrate for much longer than in areas built on firmer terrain. Experts describe this phenomenon as a “gelatin effect,” comparing the way the soil wobbles to a dish of gelatin shaking in a bowl long after the initial jolt.
This soil amplification helps explain why certain neighborhoods, particularly in the historic lakebed zone, have historically suffered the most destruction, while areas built on more stable ground nearby escape relatively unscathed. To learn more about the science behind this dangerous geological quirk, read the full article at informador.mx.
Source: El "efecto gelatina" del subsuelo en CDMX ante un sismo (informador.mx).
Image: Velella, BY-SA 4.0 (via Openverse).