Ecuador

Ecuador sits directly above the collision zone between the Nazca Plate and the South American Plate, facing the most energetic segment of the South American [[subduction-zone]] where convergence rates reach approximately 6.5 centimetres per year. The Ecuador Trench lies roughly 100 kilometres off the Pacific coast, and the locked interface between the two plates generates periodic great earthquakes and associated [[tsunami]]s that have shaped Ecuador's coastal history. The subducting Carnegie Ridge — a major aseismic volcanic ridge on the Nazca Plate formed by the Galápagos hotspot — is currently colliding with and partially subduc­ting beneath Ecuador, perturbing the [[subduction-zone]] geometry and potentially influencing both the rupture segmentation and the [[tsunami]] generation characteristics of future great earthquakes. Onshore, the Andean volcanic arc includes some of the most active volcanoes in South America: Cotopaxi (the world's highest active volcano at 5,897 metres), Tungurahua, Sangay, Reventador, and Pichincha all erupt periodically, generating volcano-tectonic earthquake swarms. The inter-Andean valley where Quito and Riobamba are located is bordered by active crustal faults that represent urban seismic hazards independent of the offshore [[subduction-zone]]. The Galápagos Islands to the west, on the Nazca Plate, sit above the Galápagos hotspot and experience volcanic seismicity distinct from the subduction-driven seismicity of mainland Ecuador.

Ecuador's recorded seismic history is dominated by the great 1906 earthquake — one of the largest of the twentieth century — and subsequent subduction events along the same interface. The 31 January 1906 Ecuador-Colombia earthquake (magnitude 8.5–8.8) generated a powerful [[tsunami]] that killed over 500–1,000 people along the coast and was recorded across the Pacific. Its rupture zone extended from Esmeraldas in Ecuador northward into Colombia. The 19 January 1958 earthquake (magnitude 7.8) struck the same northern Ecuador coast and generated a locally destructive [[tsunami]]. The 12 December 1979 Tumaco earthquake (magnitude 7.9) on the Colombia-Ecuador border caused 259 deaths and significant coastal damage. The 5 March 1987 Reventador earthquake (magnitude 7.1 and 6.9) struck the Amazonian foothills of northeastern Ecuador, triggering massive landslides that severed the Trans-Ecuadorian oil pipeline and caused economic losses estimated at over 1 billion dollars — a reminder that even moderate earthquakes in steep Andean terrain can have outsized economic consequences. The 16 April 2016 Pedernales earthquake (magnitude 7.8) struck the northern coast near the city of Pedernales, killing 676 people and destroying thousands of buildings; the [[epicenter]] was shallow and the shaking was intensified by coastal sediments, making it Ecuador's deadliest earthquake in recent decades.

Ecuador's tectonic framework reflects the same broad Andean subduction system that runs the length of western South America, but with distinctive complications from the Carnegie Ridge collision and the presence of the Galápagos microplate to the west. The Carnegie Ridge — a chain of elevated oceanic crust produced by the Galápagos hotspot as the Nazca Plate passed over it — is approximately 200 kilometres wide and stands 2 kilometres above the surrounding ocean floor; its partial subduction beneath Ecuador modifies the coupling of the [[subduction-zone]] interface and is associated with the historical concentration of large earthquakes in the northern Ecuador-southern Colombia segment. The inter-Andean valley (Sierra), the geological expression of a structural graben between the Western and Eastern Cordilleras, contains numerous active normal and reverse faults related to crustal deformation within the Andean wedge. Quito, Ecuador's capital, sits in the Sierra within reach of both the offshore [[subduction-zone]] and the Quito Fault System, which runs almost directly beneath the city. Paleoseismological trenching of the Quito Fault has revealed evidence of multiple large prehistoric earthquakes, suggesting a recurrence that makes future urban hazard in Quito a serious concern. [[aftershock]] sequences following major Ecuadorian earthquakes can last months; the 2016 Pedernales sequence included several M6+ events. Ecuador's Instituto Geofísico (IG-EPN) operates the national seismological and volcanic monitoring network.