Arica after the earthquake and tsunami USS Wateree]] beached at Arica, inland Sketches of Arica after the earthquake and tsunami from the Illustrated London News The 1868 Arica earthquake was an earthquake that occurred on August 13, 1868, near Arica, then part of Peru, now part of Chile, at 21:30 UTC. It had an estimated magnitude between 8.5 and 9.0. A tsunami (or multiple tsunamis) in the Pacific Ocean was produced by the earthquake, which was recorded in Hawaii, Japan and New Zealand.^[1]

Tectonic setting

The earthquake occurred along the boundary between the Nazca Plate and the South American Plate. The earthquake is likely to be a result of thrust-faulting, caused by the subduction of the Nazca plate beneath the South American plate.^[2]

The coastal parts of Peru and Chile have a history of great megathrust earthquakes originating from this plate boundary, such as the 1960 Valdivia earthquake.

Damage

The earthquake caused the almost complete destruction of Arica, Tacna, Moquegua, Mollendo, Ilo, Iquique, Torata and Arequipa,^[1][3] giving rise to an estimated 25,000 casualties.^[4]

The tsunami drove three ships that had been anchored in the port nearly 800 m inland: the 1560-ton Peruvian corvette America, the U.S. gunboat Wateree and the U.S. store ship Fredonia, which was completely destroyed in the process.^[1][3] The English brig Cha arcillo and two Chilean schooners, Rosa Rivera and Regalon were also lost.^[5] The tsunami also caused the near complete destruction of the port city of Pisco.^[6]

The tsunami caused considerable damage in Hawaii, washing out a bridge along the Waiohi river. In New Zealand, substantial damage occurred on the Chatham Islands and the Banks peninsula with many houses washed away and boats damaged, but only one death was recorded.^[1]

Characteristics

Earthquake

Two separate earthquakes have been described,^[7] but they may both be referring to the same event.^[4]

The earthquake was felt over a very wide area, up to 1400 km to the northwest in Samanco, Peru and 224 km to the east in Bolivia. Estimates of its magnitude range from 8.5 to 9.0. A 600 km rupture length has been estimated from the pattern of isoseismals making it one of the largest fault breaks in modern times.^[6]

About 400 aftershocks were recorded by 25 August of that year.^[1]

Tsunami

Although this event generated a tsunami that was noted across the Pacific, most of the associated damage was localised along the coasts of southern Peru and what is now northernmost Chile.^[2] The first wave arrived at Arica 52 minutes after the earthquake, with a 12 m height, followed by the largest 16 m wave 73 minutes later.^[3]

Future risk

The Arica area forms part of a seismic gap between 15 and 24 S, with no major earthquake after 1877. In accordance with this theory "a strong event is likely to occur in the near future".^[2] An earthquake affecting the same sector of the plate boundary as the 1868 event with a magnitude of 8.6 has been forecast as likely to occur by 2010.^[3] A repeat of the 1868 event would probably cause more casualties, because of the increase of population in areas at risk.

References

A book is dedicated to this earthquake: Manuel Fern ndez Canque, Arica 1868, un tsunami y un terremoto Coedici n Centro de Investigaciones Barros Arana y Universidad de Tarapac , Arica, Santiago de Chile 2007 pp. 332, ISBN 978-956-244-194-0

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