Peru lies above the destructive boundary where the Nazca Plate is being subducted beneath the South American Plate. The two plates are converging towards each other at a rate of about 78mm or 3 inches per year. Southwestern Peru has a history of very large earthquakes. The June 23 shock originated just southeast of the source of a magnitude 7.7 earthquake that occurred in 1996, and it appears to have involved rupture of part of the plate boundary segment that produced an earthquake of magnitude approximately 9.0 in 1868. The 1868 earthquake was destructive in towns that were heavily damaged in the June 23 earthquake. The 1868 earthquake produced a tsunami that killed thousands of people along the South American coast and also caused damage in Hawaii and the only recorded tsunami deaths in New Zealand.
Earthquake
The earthquake occurred as a result of thrust faulting along the plate boundary interface. The initial onset consisted of two events separated by about 6 seconds. It was followed by at least one larger complex event occurring about 40 seconds later. The rupture area as determined from the distribution of aftershocks was 320 km x 100 km. The rupture propagated unilaterally from the hypocenter towards the southeast.
Damage and casualties
At least 74 people were killed, including 26 killed by a tsunami. At least 2,687 were injured, 17,510 homes were destroyed and 35,549 homes damaged in the Arequipa-Camana-Tacna area. An additional 64 people were missing due to the tsunami in the Camana-Chala area. Landslides blocked highways in the epicentral area. Many of the historic buildings in Arequipa were damaged or destroyed, including the left tower of the Basilica Cathedral of Arequipa. Some people were injured and damage was reported in the Arica, Chile area. It was felt in Arica, Iquique, Calama and Tocopilla, Chile. The quake was also felt strongly in much of southern Peru and northern Chile and also in Bolivia. Tsunami runup heights near Camana were estimated from field evidence to have reached approximately 7m at some locations; at other locations, the tsunami inundation distance extended more than 1 km inland from the coast. Tsunami wave heights recorded from selected tide stations: 2.5m at Arica; 1.5m at Iquique; 1.0m at Coquimbo, Chile.
