The 2016 Quellón Earthquake and Seismicity in Southern Chile

On December 25, 2016, at 14:22 local time, a magnitude 7.6 earthquake struck 41 km southwest of Quellón, Chile, at a depth of 38 km. This event occurred in a region of intense tectonic activity along the Nazca-South American plate boundary. The earthquake was felt across Chiloé Island and parts of mainland Chile, prompting evacuations and minor structural damage but resulting in no reported fatalities.

Southern Chile lies within the Pacific Ring of Fire, where the oceanic Nazca Plate subducts beneath the continental South American Plate at a rate of approximately 6–7 cm per year. This convergent margin produces frequent megathrust earthquakes. The 2016 event originated on the interface between these plates, consistent with typical subduction-zone seismicity. The hypocentral depth of 38 km placed it in the upper portion of the seismogenic zone, where brittle failure generates strong ground shaking.

The broader geological history of the area includes some of the largest recorded earthquakes. The 1960 Valdivia earthquake, with a magnitude of 9.5, nucleated nearby and remains the most powerful instrumentally recorded event worldwide. Subsequent large events, such as the 2010 Maule earthquake (M8.8), demonstrate the persistent strain accumulation and release along this segment of the subduction zone. The 2016 Quellón earthquake fits within this pattern of recurrent moderate-to-large events that relieve stress without necessarily triggering a great earthquake.

Post-event analysis indicated that the rupture propagated along a roughly 100 km segment of the plate interface. Aftershocks clustered both near the mainshock hypocenter and to the northeast, reflecting stress transfer within the subduction complex. The region’s geology features accreted sedimentary rocks, volcanic arcs, and active fault systems that amplify local seismic hazards.

Quellón, situated on the southern tip of Chiloé Island, sits above a locked portion of the subduction zone that has accumulated significant strain since the 1960 event. Ongoing monitoring by Chile’s National Seismological Center continues to track microseismicity and deformation to refine hazard assessments for the area.

References

USGS Earthquake Catalog National Seismological Center of Chile (CSN) reports