More than a month after a magnitude 7.4 earthquake rattled Colombia’s Chocó department on August 10, the ground still won’t sit still. On Sunday, September 14, the Colombian Geological Survey recorded several tremors above magnitude 4.0 centered near Istmina, a town in Chocó, with three quakes striking within just six minutes that afternoon—magnitudes 4.9, 4.4, and 4.1. An hour later, another 4.9 quake hit the same area. All were felt as far away as Valle del Cauca, Risaralda, Antioquia, and Tolima, generating more than 2,000 reports from residents who felt the shaking.
Freddy Tovar, who coordinates Colombia’s National Seismological Network, explained that scientists are tracking two separate patterns since August’s major quake. One is a classic aftershock sequence, with tremors occurring 70 to 120 kilometers (roughly 43 to 75 miles) underground. The other is what’s called a seismic swarm—the pattern behind Sunday’s activity.
Unlike aftershocks, which gradually weaken after one dominant main shock, a swarm has no single defining event. Instead, Tovar said, quakes of varying strength occur steadily over time, which explains why the shaking hasn’t tapered off. He noted that such swarms can last days, weeks, or even months before finally subsiding.
Curious about the science behind Chocó’s ongoing tremors? Check out the full report at El Tiempo.
Source: ¿Por qué sigue temblando en Chocó? Esto explica el Servicio Geológico sobre el enjambre sísmico (eltiempo.com). English version produced with AI assistance.
Image: James St. John, BY 2.0 (via Openverse).