On January 1, 1996, at 4:05 p.m. Central Indonesia Time, an earthquake with an epicenter in the

Makassar Strait Makassar Strait is a strait between the islands of Borneo and Sulawesi in Indonesia. To the north it joins the Celebes Sea, while to the south it meets the Java Sea. To the northeast, it forms the Sangkulirang Bay south of the Mangkalihat Pe ...

struck north of

Minahasa The Minahasans (alternative spelling: Minahassa) are an ethnic group native to the North Sulawesi province of Indonesia, formerly known as North Celebes. The Minahasa people sometimes refer to themselves as Manado people. Although the Minahasan p ...

on the island of Sulawesi,

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

. The earthquake measured 7.9 on the

moment magnitude scale 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 ...

and was centered off Tolitoli Regency in

Central Sulawesi Central Sulawesi ( Indonesian: ''Sulawesi Tengah'') is a province of Indonesia located at the centre of the island of Sulawesi. The administrative capital and largest city is located in Palu. The 2010 census recorded a population of 2,635,009 fo ...

, or 25 km from the Tonggolobibi village. A

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

of was triggered by this earthquake as a result. At least 350 buildings were badly damaged, nine people died and 63 people were injured.

Tectonic setting

The North Sulawesi Trench is a subduction zone parallel to the

Minahasa Peninsula The Minahasa Peninsula, also spelled Minahassa, is one of the four principal peninsulas on the Indonesian island of Sulawesi. It stretches north from the central part of the island, before turning to the east and forming the northern boundary of th ...

where the Sunda Plate dives beneath the

Molucca Sea Plate Located in the western Pacific Ocean near Indonesia, the Molucca Sea Plate has been classified by scientists as a fully subducted microplate that is part of the Molucca Sea Collision Complex. The Molucca Sea Plate represents the only known example ...

at a rate of 4 cm/yr. Here, three major tectonic plates, the

Sunda Sunda may refer to: Europe * Sunda, Faroe Islands India * Sunda (asura), an asura brother of Upasunda * Sunda (clan), a clan (gotra) of Jats in Haryana and Rajasthan, India Southeast Asia * Sundanese (disambiguation) ** Sundanese people ...

Australian Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal A ...

and Philippine Sea Plates interact in a complex manner, broken up into several smaller microplates. The North Sulawesi Subduction Zone joins the

Palu-Koro Fault The Palu-Koro Fault or Palu-Koro Fault System is a major active NNW-SSE trending left-lateral strike-slip fault zone on the island of Sulawesi in Indonesia. It caused the 2018 Sulawesi earthquake and tsunami. Geometry It extends from near Dondow ...

at its westernmost tip.

Earthquake

The

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

which this earthquake occurred along had a very shallow dip angle of 7°, during the event, a section of it had ruptured. An average slip was estimated at 1.8 meters. The earthquake took place along a relay zone between the North Sulawesi Trench and

. The strike-slip component of this oblique-thrust event was a result of interaction with the Palu-Koro Fault. The rupture process took roughly 30 seconds. On Pangalasean Island, uplift of was determined. Two aftershocks in July, a magnitude 6.6 and 7.0 on the 16th and 22nd struck about 50 km northeast of the January mainshock. This event was larger but far less deadly compared to the 7.5 Sulawesi earthquake in 2018 to the south. The mainshock resulted in a large coulomb stress transfer component around the Palu-Koro Fault. Many additional aftershocks were triggered along the Palu-Koro Fault following the mainshock. There was also an increased rate in seismicity around the island after the 1996 shock. A number of magnitude 6.0+ earthquakes occurred along the fault and was triggered after the 1996 thrust mainshock. In May and October 1998, two earthquakes measuring 6.6 and 6.0 , respectively, occurred near the Palu–Koro Fault. The former event was the result of strike-slip faulting while the latter displayed thrusting on a shallow, southeast dipping fault. Stress transfer later brought the Palu-Koro Fault closer to

rupture Rupture may refer to: General * Rupture (engineering), a failure of tough ductile materials loaded in tension Anatomy and medicine * Abdominal hernia, formerly referred to as "a rupture" * Achilles tendon rupture * Rupture of membranes, a "wate ...

and eventually failed, causing the 2018 earthquake.

Tsunami

The tsunami inundated more than 100 km of coastline along with Northern Sulawesi between 5–10 minutes after the tremor. The run-up heights of these waves were between , according to eyewitness. More than 400 houses in the village of Tonggolobibi were destroyed when the waves swept through.
The water destroyed 183 houses and damaged 228 units around the Bangkir-Tolitoli area. About of coastline was affected, there were no reports of the tsunami recorded outside of Sulawesi, thus inferring that the tsunami was localized. The tsunami penetrated up riverbeds and carried five boats, including two 500-ton motorboats 250 meters onshore. Since the tsunami occurred during a high tide of , and there was subsidence of the land of about , estimating the height of the tsunami was challenging.

References

{{Earthquakes in Indonesia 1996 earthquakes Earthquakes in Indonesia Tsunamis in Indonesia 1990s floods in Asia 1996 floods 1996 in Indonesia January 1996 events in Asia History of Sulawesi 1996 disasters in Indonesia 1996 tsunamis

Tectonic setting

Earthquake

Tsunami

See also

References