Tectonic Summary

The July 19, 2024, M 7.4 earthquake near Atacama, Chile occurred as the result of normal faulting. The earthquake occurred at an intermediate depth within the subducted Nazca plate, at a depth of about 120 km under the triple country borders between Chile, Argentina, and Bolivia. Focal mechanism solutions for the earthquake indicate that rupture occurred on either a steeply or shallowing dipping normal fault within the interior of the subducted Nazca slab. Slip on a fault of either orientation would accommodate the down-dip extension of the Nazca slab as it bends downward beneath South America. At the location of the earthquake, the Nazca plate moves eastward with respect to the South America plate, subducting at the Peru-Chile Trench along the South America coastline at velocity of about 74 mm/yr.

Earthquakes like this event with focal depths between 70 and 300 km are commonly termed “intermediate-depth” earthquakes. Although the Chilean subduction zone is well known for producing very large earthquakes along the coastline, including the 2010 magnitude 8.8 Maule earthquake and 1960 magnitude 9.5 Valdivia earthquake, large (magnitude 7 and over) intermediate depth within the subduction zone are also relatively common. Such earthquakes 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.

Intermediate-depth earthquakes reflect deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. These intermediate depth earthquakes commonly occur near regions where the subducted slab bends - normal faulting earthquakes occur where the slab bends downward and induces extension in the upper half of the subducted slab. The distance of intermediate depth earthquakes from the coastline in Chile can vary considerably owing to along-strike variations in the dip of the subducting slab. In the vicinity of the July 19 earthquake, the subducting Nazca plate begins transitioning to a flatter dip, so intermediate depth earthquakes occur further inland than they typically occur in northern Chile. “Deep-focus” earthquakes (greater than 300 km deep) also occur in the subducted Nazca plate beneath central Argentina, Bolivia, and Brazil. Earthquakes have been reliably located to depths greater than 600 km in this region. Over the preceding century there have been seven other M 7.0 or larger earthquakes within 250 km of the July 19th event, the largest being a M8.2 on December 9th, 1950 which occurred at a depth of 114 km. Some intermediate depth normal faulting earthquakes in Chile have produced damage, including an M7.8 earthquake in northern Chile in 2005 that caused over 200 injuries.

Event Details

Event Map

Tectonic Summary

Historical Magnitude 4.5+ (100km)

Tectonic Summary

Historical Magnitude 4.5+ (100km)