M 7.5 - 115 km ESE of Palora, Ecuador

Tectonic Summary

The February 22, 2019, M 7.5 Ecuador earthquake occurred as the result of normal faulting at an intermediate depth, approximately 130 km beneath western Ecuador within the lithosphere of the subducted Nazca plate. Focal mechanism solutions indicate that rupture occurred on either a steeply dipping normal fault or a shallowly dipping normal fault, both striking in an approximate NW-SE direction. Slip on a fault of either orientation would accommodate the down-dip extension of the Nazca slab. At the location of the earthquake, the oceanic Nazca plate moves east relative to the South America plate at a rate of about 70 mm/yr, subducting at the Peru-Chile Trench west of the Ecuadoran coast and sinking into the mantle beneath South America. Like most earthquakes of Ecuador and western South America, this event was caused by strains generated by the ongoing subduction process.

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed “intermediate-depth” earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. “Deep-focus” earthquakes, those with focal depths greater than 300 km, also occur in the subducted Nazca plate farther east from the Peru-Chile Trench, beneath western Brazil and central Argentina. Earthquakes have been reliably located to depths of about 650 km in this region.

The Peru-Chile Trench is an area that hosts large earthquakes quite regularly. Within 500 km of the February 22nd earthquake, there have been 15 other intermediate depth earthquakes with magnitudes of 6.5+ over the preceding century. Today’s earthquake is the largest of these; another M 7.5 event occurred about 400 km to the south-southeast beneath Peru in September 2005. A M 7.4 earthquake in the Peru-Ecuador border region in July 1971, 80 km to the southwest of the February 22, 2019, event at a depth of 120 km, was previously the largest known intermediate depth earthquakes in Ecuador since 1900. A M 7.1 earthquake about 110 km to the north-northwest of the February 22, 2019 event in August 2010 caused minor damage across Ecuador, including in the coastal city of Guayaquil.