By: USGS.gov

On June 23, 2001, M 8.4 earthquake near the coast of southern Peru occurred as the result of thrust faulting on the plate boundary interface 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 June 23rd earthquake. This great-sized earthquake resulted in many casualties, the majority of which were associated with the subsequent tsunami and landsliding.

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 that was 630 km deep near the Peru-Bolivia border in 1994.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Thrust-faulting events of the size of the June 23, 2001, earthquake are typically about 260x100 km (length x width); modeling of this earthquake implies dimensions of about 150–200x150 km, predominantly southeast of the hypocenter.

Southwestern Peru has a history of very large earthquakes. In November 1996, a M 7.7 earthquake ruptured part of the plate boundary to the northwest of the June 23rd event. This plate boundary segment is also thought to have ruptured in an earthquake of about M 8.8 in 1868. The 1868 event was destructive in the same towns that were heavily damaged in the June 23rd earthquake, and produced a tsunami that resulted in thousands of fatalities along the South America coast and also caused damage in Hawaii and alarm in Japan. The June 23, 2001, earthquake was a complex event with an initial onset of one or more moderate to large subevents followed by at least one larger complex event about 40 seconds later.

The June 23, 2001, M 8.4 earthquake near the coast of southern Peru occurred as the result of thrust faulting on the plate boundary interface 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 June 23rd earthquake. This great-sized earthquake resulted in many casualties, the majority of which were associated with the subsequent tsunami and landsliding.

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 that was 630 km deep near the Peru-Bolivia border in 1994.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Thrust-faulting events of the size of the June 23, 2001, earthquake are typically about 260x100 km (length x width); modeling of this earthquake implies dimensions of about 150–200x150 km, predominantly southeast of the hypocenter.

Southwestern Peru has a history of very large earthquakes. In November 1996, a M 7.7 earthquake ruptured part of the plate boundary to the northwest of the June 23rd event. This plate boundary segment is also thought to have ruptured in an earthquake of about M 8.8 in 1868. The 1868 event was destructive in the same towns that were heavily damaged in the June 23rd earthquake, and produced a tsunami that resulted in thousands of fatalities along the South America coast and also caused damage in Hawaii and alarm in Japan. The June 23, 2001, earthquake was a complex event with an initial onset of one or more moderate to large subevents followed by at least one larger complex event about 40 seconds later.

Read the full article here: M 8.4 - 6 km SSW of Atico, Peru 

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