Colombia's Chocó Hit by Repeated Seismic Swarms After Deadly Quake

Colombia's Chocó department experienced another intense seismic swarm on September 16, with five tremors recorded between 3:12 p.m. and 4:05 p.m. local time. Magnitudes ranged from 3.3 to 4.7 at depths of 37 to 46 kilometers, centered near Medio San Juan, Sipí, and Istmina.

The Colombian Geological Service (SGC) distinguishes this activity from typical aftershocks of the August 10 magnitude 7.4 quake. That event killed 335 people and triggered roughly 300 aftershocks. SGC hazards director Mónica Arcila said the main quake altered rock structure, shifting current activity to shallow depths in the upper plate.

“The incessant repetition of these movements severely impacts the mental health of the population, which has not yet recovered from the strong earthquake suffered last August 10.”

Unlike classic aftershock sequences that decay over time, a seismic swarm features multiple events of fluctuating magnitude without a single dominant shock. Mechanisms include fluid migration and physicochemical interactions in the lithosphere. Authorities confirm no new damage or casualties from the latest swarm.

Governor Nubia Carolina Córdoba warned the incessant shaking severely impacts mental health in communities still recovering from August. Over 2,000 citizen reports logged tremors felt across Chocó, Valle del Cauca, Risaralda, Antioquia, and Tolima. Residents like Erick David Guevara Ortiz in Istmina describe living in constant fear.

Earlier on September 14, seven quakes struck Sipí in the morning, followed by three events above magnitude 4.0 in Istmina within six minutes. Scientists emphasize that swarm activity does not "release" enough energy to prevent a larger earthquake, debunking a common myth.