Shortly after midnight local time on January 20 (January 19,

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

), 1981, eastern Indonesia was struck by an earthquake known as the 1981 Irian Jaya earthquake. Registering a moment magnitude of 6.7, it killed more than 300 people, damaging structures and buildings across the

Irian Jaya New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is separated from Austral ...

province. Indonesia is highly active in terms of seismicity and volcanic eruptions, with a

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

zone and many faults. It is neighbored by several

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

s. Such earthquakes pose a significant threat to life in the area through earthquakes and also tsunamis.

Geology

Indonesia, one of the most seismically active places in the world, hosts hundreds of islands, many with volcanoes. It is an

island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...

, composed by a

zone (in the Sunda Trench) and islands. Unlike most subduction zones, the Sunda Trench is parallel to the chain of islands to which it corresponds, creating

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

faulting. Indonesia itself is surrounded by multiple

tectonic plates Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

– namely the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

, the Southeast Asia lithospheric, and the Indo-Australian plates – causing it to be a so-called hotspot for both seismic and volcanic activity. The epicenter was in

Papua Province Papua is a province of Indonesia, comprising the northern coast of Western New Guinea together with island groups in Cenderawasih Bay to the west. It roughly follows the borders of the Papuan customary region of Tabi Saireri, and is divided in ...

, in the Irian Jaya Province. The orientation and type of faulting is uncertain, due to a poorly constrained

focal mechanism The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...

but is thought to have been a

reverse fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic f ...

Damage and casualties

Spawning enormous landslides, the earthquake left at least 305 people dead and more than 1,000 missing. Entire villages were covered by debris. It was described as "strong" by ''

The New York Times ''The New York Times'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of ...

''. The earthquake caused huge landslides, which cascaded into the villages below the mountains, destroying more than 150 homes. The debris from these flows blocked transportation by road, "cutting off more than 2,000 area residents". Relief efforts took several days.

Future threats

Indonesia is known for deadly earthquakes, primarily the

2004 Indian Ocean earthquake and tsunami On 26 December 2004, at 07:58:53 local time ( UTC+7), a major earthquake with a magnitude of 9.2–9.3 struck with an epicentre off the west coast of Aceh in northern Sumatra, Indonesia. The undersea megathrust earthquake, known in the sci ...

, which killed more than 227,000 people. Earthquakes along the subduction zone at Sunda and on the

Great Sumatran fault The Great Sumatran fault, also known as Semangko fault, is a large strike-slip fault running the entire length of the island of Sumatra. This Indonesian island is located in a highly seismic area of the world, including a subduction zone off th ...

pose a serious threat to life, especially in the form of tsunamis. A 2005 study found that stress on at least these two zones was at a heightened level, and both have been active. The Sunda Trench zone has since produced the

2006 Pangandaran earthquake and tsunami An earthquake occurred on July 17, 2006, at along a subduction zone off the coast of West Java, west and central Java, a large and densely populated island in the Indonesian archipelago. The shock had a Moment magnitude scale, moment magnitude ...

, while the Great Sumatran fault has not produced an earthquake since the 2004 event.

References

External links

* {{Earthquakes in Indonesia Irian Jaya Earthquake, 1981 Irian Jaya, 1981 Irian Jaya Earthquake, 1981 Irian Jaya Earthquake, 1981 Irian Jaya earthquake Landslides in Indonesia Irian Jaya earthquake

Geology

Damage and casualties

Future threats

See also

References

External links