Shortly after midnight local time on January 20 (January 19, UTC), 1981, eastern Indonesia was struck by an earthquake known as the 1981 Irian Jaya earthquake. Registering a

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

of 6.7, it killed more than 300 people, damaging structures and buildings across the

Irian Jaya New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torres ...

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

subduction zone Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

and many faults. It is neighbored by several

tectonic plate Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

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 chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

, composed by a

(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 (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

– 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 definition, to Antarctica) in the south, and is bounded by the continen ...

, the Southeast Asia lithospheric, and the

Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...

s – 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 Papuan customary region of Tabi Saireri. It is bordered by the ...

, 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 deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

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 ...

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'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...

''. 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 An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time (UTC+7) on 26 December 2004, with an epicentre off the west coast of northern Suma ...

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

Great Sumatran fault The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction, subduction zone off the west coast of the island, Sumatra also has a large Fault (geology)#Strike-slip faults, strike-slip fault, 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 and central Java, a large and densely populated island in the Indonesian archipelago. The shock had a moment magnitude of 7.7 and a maximum perceived inten ...

, 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