M 7.6 - 51 km SW of Punta de Bombón, Peru

Tectonic Summary

The July 7, 2001, M 7.6 earthquake near the coast of southern Peru occurred as the result of shallow thrust faulting on the plate boundary between the Nazca and South America plates. At the location of the earthquake, the Nazca plate moves towards the east-northeast with respect to South America at a velocity of about 78 mm/yr and begins its descent into the mantle at the Peru-Chile Trench, to the southwest of the July 7th earthquake. This large earthquake can be considered part of the aftershock sequence of the June 23, 2001, M 8.4 earthquake, whose epicenter was located approximately 200 km to the northwest of the July 7th event.

Subduction zones such as the South America Arc are geologically complex and generate numerous earthquakes from a variety of tectonic processes that in turn cause deformation of the western edge of South America. Crustal deformation and subsequent mountain building in the overriding South America plate generate shallow earthquakes. Slip along the dipping interface between the two plates generates frequent, and often large, interplate thrust earthquakes between depths of approximately 10 and 60 km. Since 1900, numerous M 8+ earthquakes have occurred on the interface between the Nazca and South America plates, including the 1960 M 9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world, and the 2010 M 8.8 earthquake immediately to the north of the 1960 quake. Earthquakes can also be generated to depths greater than 600 km from internal deformation of the subducting Nazca plate, and the slab down-dip of the June 23rd event hosted the largest deep earthquake on record to date—a M 8.2 event 630 km deep near the Peru-Bolivia border in 1994.

Modeling of the slip history of the July 7th earthquake indicates that it broke a small section of the plate boundary approximately 60 km long and about 60 km wide at the southeast end of the larger June 23rd rupture. Between the dates of the two major events, almost 60 other aftershocks of M 5 or larger occurred in this region.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)