Quito's earthquakes are the result of a system of fault lines which go from the south of Quito to San Antonio de Pichincha—about 37 miles long, explained Alexandra Alvarado, director of the Ecuador Geophysical Institute.
“Quito's fault line is the rupture on which the city moves,” said Alvarado to El Telegrafo. “Quito's rupture was produced as the Nazca tectonic plate was advancing below the continent, generating a lot of pressure on the continent, resulting in the creation of ruptures like Quito's.”
Just like Chile, Peru and Colombia, Ecuador is a subduction zone, meaning earthquakes occur inland, where big masses of land are interacting between each other, producing these ruptures.
The ruptures are not visible on the surface, but the city of Quito lies on a fault line. An earthquake occurs when these fault lines are displaced, either within the system itself, or when another rupture is created somewhere else.
As Quito is located on the top of the Chillos and Tumbaco valleys, as they rise, Quito rises even higher—about 500 meters higher in a continuous process of about 1 million year.
“We are talking of a 1-million-year continuous process of earthquakes and reliefs,” explained the scientist. “Aftershocks correspond to the time the rocks are accommodating themselves, where the rupture occurred, leaving the area unstable, usually between 5 and 10 kilometers deep, on an inclined plan.”