2021 Flores earthquake

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2021 Flores earthquake
2021-12-14 Flores Sea M7.3 earthquake shakemap (USGS).jpg
Indonesia relief location map.jpg
Bullseye1.png
UTC  time2021-12-14 03:20:24
ISC  event 621629136
USGS-ANSS ComCat
Local date14 December 2021 (2021-12-14)
Local time11:20:24 WITA
Magnitude7.3–7.4 Mw [1] [2]
Depth16.1 km (10.0 mi)
Epicenter 7°36′11″S122°12′00″E / 7.603°S 122.200°E / -7.603; 122.200 [1]
Type Strike-slip
Areas affectedIndonesia
Total damageModerate
Max. intensity VI (Strong) [2]
Tsunami7 cm (2.8 in)
Aftershocks896 (as of 20 December 2021)
Casualties1 dead, 173 injured

An earthquake occurred 112 km, offshore, north of Maumere in the Flores Sea on 14 December. [1] The quake had a moment magnitude (Mw ) of 7.3 according to the United States Geological Survey (USGS). One person was killed and 173 others suffered injuries.

Contents

Earthquake

Initially a magnitude 7.7, it was downgraded to 7.3. [3] The quake was the result of shallow strike-slip faulting within the shallow crust beneath the Flores Sea. According to the USGS, the earthquake rupture was on an east northeast-west southwest fault with a right-lateral strike-slip motion.[ citation needed ]

A finite fault model by the ANSS indicate rupture along a fault measuring 90 km by 15 km with a maximum coseismic slip of 4.0 meters. [1] A professor at the Bandung Institute of Technology said the seismogenic fault may have been 80 km to 110 km long, and up to 30 km deep. Coseismic slip might have been 2.3 meters across the rupture area. [4]

Within the epicenter region of the quake are eight known faults—the 2021 event did not occur on any of those. This region of Indonesia is also not as seismically active, hence many expert seismologists did not expect a large earthquake to occur. The strike-slip mechanism was also unusual as thrust faulting is the dominant mechanism for earthquakes in the area. [5] Scientists at the Earth Observatory of Singapore said the fault marked the boundary between two blocks of crust; the north block moving right, relative to the block south of the fault. In 2007, the fault generated a magnitude 5.1 quake. [6]

An academic research paper in 2022 identified it as the "Kalaotoa Fault", a previously unknown structure. This strike-slip dextral fault system consists of three segments with lengths of ~100 km, ~50 km, and ~40 km, respectively. Earthquakes were also triggered on the Selayar Fault, a prominent normal fault located west of the Kalaotoa Fault, believed to be the result of stress transfer. [7] The earthquake was the largest in the region since a deep-focus Mw  7.9 struck in 1996. [8]

The shaking was reportedly most intense on the Selayar Islands, reaching a maximum Modified Mercalli intensity of VI (Strong) according to the Meteorology, Climatology, and Geophysical Agency (BMKG). [2] The earthquake was also felt V in Ranakah. [9] In Lembata, Labuan Bajo, Larantuka and Ruteng, weak shaking (III–IV) was felt. [10]

It occurred just a few days after the anniversary of a 1992 earthquake and tsunami in the same region.

Tsunami

Tsunami warnings were issued to coastal communities of the Flores region, causing panic among residents. Videos posted on social media showed panicked residents running to higher ground to avoid the anticipated waves. [11] The tsunami however, was minor, measuring only 7 centimeters (2.8 inches). [12] Warnings were cancelled two hours later at 13:20 local time. [13]

Tectonic setting

A map showing major plate boundaries of Indonesia. Plate setting Sunda megathrust.png
A map showing major plate boundaries of Indonesia.

The Flores region lie at the complex tectonic boundary between the Australian and Sunda plates, as well as several microplates. Among the major active faults are the Flores Back Arc Thrust Fault and Sunda megathrust to accommodate the complex convergence between the tectonic plates. The Flores Back Arc Thrust formed due to the convergence between the Sunda and Australian plates, accommodating compression. The two plates converge at a rate of 80 mm/yr, in which the Sunda megathrust takes 70 mm/yr of the movement. The remaining 10 mm/yr rate is accommodated by the Flores Back Arc Thrust Fault. It runs off the north coast of the Lesser Sunda Islands, in the Banda Sea. [14]

The event itself did not occur on the Sunda megathrust subduction boundary, nor did it occur on the Flores Back Arc Thrust Fault, based on inferring the focal mechanism. In the early 19th-century, the Flores Back Arc Thrust Fault also produced the large earthquakes and tsunamis in 1820 and 1815. More recently, it was responsible for the magnitude 7.8 earthquake in 1992 that triggered a devastating tsunami, as well as the 2018 Lombok earthquakes. [15] [16]

Impact

Hundreds of residents were displaced in Selayar Islands due to the quake Hundreds evacuated after a magnitude 7.4 struck Flores.jpg
Hundreds of residents were displaced in Selayar Islands due to the quake

The Selayar and Flores islands were worst affected by the earthquake; 5,064 people were displaced, according to the Indonesian National Board for Disaster Management (BNPB). An estimated 266 of the total displaced were from the Sikka Regency of East Nusa Tenggara. [17] Three school buildings, two mosques, two places of worship and a village office were also damaged. [18] Damage to buildings included roof collapse, toppled concrete walls of fence and homes and collapse of entire homes. [19]

A total of 357 houses were severely damaged, while 800 others and 24 government buildings were damaged. At least 173 people were injured, 119 of them seriously. [20] [21] Some were injured when falling in a panic caused by the tsunami warning system. [22] [23] [24] On 23 December, an elderly man with severe head injuries after being hit by falling debris died at the hospital while receiving treatment. [25] At least one of the injured was from East Nusa Tenggara while the rest were in South Sulawesi. [26]

Aftermath

Residents in South Sulawesi and the Flores region were told not to immediately enter their homes, but to inspect for damages first. While the tsunami warnings were rescinded, the BMKG warned of potentially damaging aftershocks that could collapse already weakened homes. An official from the BMKG advised people in the affected areas to avoid approaching cliffsides or the mountains due to potential rockfall and landslide risks. [15]

By 20 December, at least 16,593 villagers in the Selayar Islands were evacuated from their homes either due to damaged homes or the fear of aftershocks. The BNPB supported the supply of aid to residents including meals and refugee tents. Tranined individuals were also sent to the affected regions to attend to traumatized residents. The BNPB said a team would be flown-in to assess the damage on the islands. Given to the local government were 250 million rupiahs in relief fund from the BNPB as well. [27]

See also

Related Research Articles

<span class="mw-page-title-main">Flores</span> Island of the Lesser Sunda Islands in Indonesia

Flores is one of the Lesser Sunda Islands, a group of islands in the eastern half of Indonesia. Administratively, it forms the largest island in the East Nusa Tenggara Province. Including Komodo and Rinca islands off its west coast, the land area is 14,731.67 km2, and the population was 1,878,875 in the 2020 Census ; the official estimate as of mid-2023 was 1,962,405. The largest towns are Maumere and Ende. The name Flores is of Portuguese origin, meaning "Flowers".

The 1982 Flores earthquake struck the island of Flores in Indonesia on December 25. Registering a moment magnitude of 5.9, according to the International Seismological Centre, it created landslides and was reportedly accompanied by a tsunami. The earthquake killed thirteen people and left 390 injured, also destroying 1,875 houses and 121 other buildings. The villages of Layahong and Oyong Barang were damaged by seven seconds of shaking.

<span class="mw-page-title-main">2017 Java earthquake</span> 2017 earthquake centered in Tasikmalaya, West Java, Indonesia

The 2017 Java earthquake occurred on 15 December 2017 when a moment magnitude 6.5 earthquake struck the Indonesian island of Java, specifically the city of Tasikmalaya on 23:47:58 West Indonesian Time in West Java, Indonesia. The earthquake struck at a depth of 91 km and was categorized as a strong but deep earthquake. It was initially registered as a 7.3 magnitude earthquake by Indonesian agencies. Widespread damage was reported across Tasikmalaya, the nearest major city to the epicentre. A tsunami warning was immediately issued by the authorities but was subsequently cancelled. Four people have been confirmed dead.

<span class="mw-page-title-main">July 2018 Lombok earthquake</span> Earthquake that occurred in July 2018 in Indonesia

A Mw 6.4 earthquake struck the island of Lombok on the morning of 29 July 2018 at a shallow depth of 14 km (8.7 mi). Widespread damage was reported in the area, and authorities confirmed that 20 people were killed in the earthquake while hundreds were injured.

<span class="mw-page-title-main">5 August 2018 Lombok earthquake</span> Earthquake in Indonesia

On 5 August 2018, a destructive and shallow earthquake measuring Mw  6.9 struck the island of Lombok, Indonesia. It was the main shock following its foreshock, a nearby Mw  6.4 earthquake on 29 July. It was followed by a nearby 6.9 earthquake on 19 August 2018.

<span class="mw-page-title-main">2018 Sulawesi earthquake and tsunami</span> 7.5 Mw earthquake Landslide and tsunami in Indonesia

On 28 September 2018, a shallow, large earthquake struck in the neck of the Minahasa Peninsula, Indonesia, with its epicentre located in the mountainous Donggala Regency, Central Sulawesi. The magnitude 7.5 quake was located 70 km (43 mi) away from the provincial capital Palu and was felt as far away as Samarinda on East Kalimantan and also in Tawau, Malaysia. This event was preceded by a sequence of foreshocks, the largest of which was a magnitude 6.1 tremor that occurred earlier that day.

<span class="mw-page-title-main">2018 East Java earthquake</span> Earthquake affecting Indonesia

On 11 October 2018, an earthquake struck off the coast of East Java, Indonesia, with the epicentre located off the coast of Situbondo Regency. The earthquake, which struck at dawn, killing four people in addition to destroying or damaging hundreds of houses, mostly on the small island of Sapudi.

On 17 March 2019, an earthquake measuring Mw  5.6 struck the island of Lombok in West Nusa Tenggara, Indonesia. The earthquake triggered a landslide, killing six and injuring nearly 200 others.

<span class="mw-page-title-main">2019 North Maluku earthquake</span> July 14, 2019, earthquake in Indonesia

The 2019 North Maluku earthquake, a shallow 7.2 magnitude earthquake, struck the island of Halmahera, North Maluku, Indonesia on 14 July 2019 at 18:10 local time with its epicentre located at South Halmahera. It struck at a shallow depth of 10 km (6.2 mi) near Labuha, a small port town located in Bacan Island. The earthquake produced a non-destructive 20 cm tsunami, which struck Labuha just minutes after the shaking started. 14 people were killed by the earthquake while 129 people were injured, and more than 50,000 people were displaced. The earthquake inflicted a total damage of Rp 238 billion.

<span class="mw-page-title-main">2019 Sunda Strait earthquake</span> 2 August 2019, earthquake in Indonesia

The 2019 Sunda Strait earthquake occurred on the night of 2 August 2019, when a magnitude 6.9 earthquake rattled Sunda Strait at a moderate depth of 52.8 kilometres. The epicentre was located 214 km from Bandar Lampung, the capital of Lampung and 147 km west of Sumur, Pandeglang Regency. The earthquake struck with a maximum intensity of VI (Strong). The earthquake prompted a tsunami warning in the area, with authorities urging coastal residents to immediately evacuate to higher grounds.

<span class="mw-page-title-main">2019 Ambon earthquake</span> Earthquake affecting Maluku, Indonesia

On 26 September 2019, a strong magnitude 6.5 earthquake struck Seram Island in Maluku, Indonesia, near the provincial capital of Ambon. The earthquake struck at 07:46:44 Eastern Indonesia Time with a shallow depth of 18 km. The tremor could be felt throughout the island, with an intensity of very strong (VII) reportedly felt in the provincial capital of Ambon.

A moment magnitude 6.2 earthquake struck Majene Regency in West Sulawesi, Indonesia, on 15 January 2021, at 02:28 WITA. The reverse faulting shock initiated at 18.0 km (11.2 mi) depth with an epicenter inland, located 32 km (20 mi) south of Mamuju. It was preceded by a Mw  5.7 foreshock several hours prior. Shaking from the mainshock was assigned a maximum Modified Mercalli intensity of VI (Strong) in Majene and Mamuju. Four of the five regencies in West Sulawesi were affected. More than 6,000 structures were damaged or destroyed; damage was estimated at Rp829.1 billion rupiah. At least 105 people were confirmed dead; more than 3,300 were injured and thousands were displaced.

<span class="mw-page-title-main">2021 East Java earthquake</span> Earthquake in Indonesia

An earthquake occurred on 10 April 2021 at 14:00 local time (UTC+07:00) off the south coast of eastern Java. The epicenter of the earthquake is located 44 km south–southwest of Gondanglegi Kulon in East Java province. Measuring 6.0 or 6.1 on the moment magnitude scale (Mw ) and having a depth of 82.3 km, the earthquake caused moderate shaking measuring V on the Mercalli intensity scale. At least 10 individuals are known to have died from the earthquake and another 104 were seriously injured.

<span class="mw-page-title-main">Lembang Fault</span> Fault in Indonesia

The Lembang Fault is an active fault located 10 km north of the city of Bandung on the Indonesian island of Java. This sinistral slip fault is estimated to measure 29 km in length. While no historical earthquakes have occurred, the fault is thought to be possible of generating a magnitude 6.5 to 7.0 earthquake in the future. Because of the potential for large and damaging earthquakes on the fault, the Meteorology, Climatology and Geophysics Agency (BMKG) has been monitoring activity on the fault.

The 1815 Bali earthquake occurred on November 22 between 22:00 and 23:00 local time (WITA), affecting the Bali Kingdom. The estimated moment magnitude 7.0 earthquake struck off the north coast of Bali at a shallow depth. It was assigned a maximum intensity of IX (Violent) on the Mercalli intensity scale, causing severe damage in Buleleng and Tabanan. The earthquake caused a landslide and tsunami that killed 11,453 people.

The 2021 Bali earthquake struck at 04:18 local time (UTC+08:00) when people were still sleeping on 15 October 2021. It resulted in 4 deaths and 73 more injured, despite having a moment magnitude of 4.7.

<span class="mw-page-title-main">2022 Sumatra earthquake</span> Earthquake in Indonesia

On 25 February 2022 at 08:39 WIB, a moment magnitude (Mw ) 6.2 earthquake struck West Sumatra, Indonesia at a depth of 4.0 km (2.5 mi). Preceded by one foreshock and followed by over 200 aftershocks, the mainshock had an epicenter at the foot of Mount Talakmau in Pasaman Regency. The mainshock was the result of strike-slip faulting along a previously unidentified segment of the Great Sumatran Fault. At least 27 people died, 457 were injured, and 19,221 others were displaced. It inflicted 780 million Indonesian rupiahs (Rp) worth of damage. The heaviest damage was recorded at three villages around Mount Talakmau. Landslides and flash floods caused additional damage and casualties.

<span class="mw-page-title-main">2022 West Java earthquake</span> Earthquake in Indonesia

On 21 November 2022, at 13:21 WIB (UTC+07:00), a Mww 5.6 earthquake struck near Cianjur in West Java, Indonesia. The strike-slip earthquake occurred with a focal depth of 11 km (6.8 mi). Between 335 and 635 people died, 7,729 were injured and five remain missing. More than 62,628 homes were damaged across 16 districts in Cianjur Regency and the surrounding region. It is the deadliest earthquake to hit Indonesia since the 2018 Sulawesi earthquake. Damage evaluated after the event earned it a maximum Modified Mercalli intensity of VIII (Severe).

References

  1. 1 2 3 4 "M 7.3 - 112 km N of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey. 14 December 2021. Retrieved 14 December 2021.
  2. 1 2 3 Wallansha, Robby (15 December 2021). "Ulasan Guncangan Tanah Akibat Gempa Bumi Di Laut Flores Nusa Tenggara Timur 14 Desember 2021" [Review of Earthquake Due to Earthquake in the Flores Sea, East Nusa Tenggara 14 December 2021]. bmkg.go.id. Meteorology, Climatology, and Geophysical Agency . Retrieved 30 April 2022.
  3. ↑ "Magnitude 7.7 earthquake strikes near Maumere, East Nusa Tenggara". The Jakarta Post. 14 December 2021. Retrieved 23 December 2021.
  4. ↑ Ahmad Arif (16 December 2021). "Gempa yang Mengingatkan Tsunami Flores 1992" (in Indonesian). Kompas . Retrieved 23 December 2021.
  5. ↑ Daryono Daryono (21 December 2021). Shierine Wangsa Wibawa (ed.). "Mengenali Jalur Sesar Pembangkit Gempa Laut Flores" (in Indonesian). Kompas . Retrieved 23 December 2021.
  6. ↑ Lauriane Chardot (16 December 2021). "The Mw 7.3 Earthquake Off the Coast of Flores Likely Occurred on a Known Fault". earthobservatory.sg. Earth Observatory of Singapore . Retrieved 23 December 2021.
  7. ↑ Supendi, Pepen; Rawlinson, Nicholas; Prayitno, Bambang Setiyo; Widiyantoro, Sri; Simanjuntak, Andrean; Palgunadi, Kadek Hendrawan; Kurniawan, Andri; Marliyani, Gayatri Indah; Nugraha, Andri Dian; Daryono, Daryono; Anugrah, Suci Dewi (1 July 2022). "The Kalaotoa Fault: A Newly Identified Fault that Generated the Mw 7.3 Flores Sea Earthquake". The Seismic Record. 2 (3): 176–185. Bibcode:2022SeisR...2..176S. doi: 10.1785/0320220015 . hdl: 10754/680058 . ISSN   2694-4006. S2CID   251264701.
  8. ↑ "M 7.9 - 112 km NNE of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey. 17 June 1996. Retrieved 24 January 2022.
  9. ↑ "Earthquake and tsunami". magma.esdm.go.id (in Indonesian). MAGMA Indonesia. 16 December 2021. Retrieved 23 December 2021.
  10. ↑ Haryanti Puspa Sari. Icha Rastika (ed.). "BMKG: Gempa M 7,4 Larantuka akibat Patahan Aktif di Laut Flores" (in Indonesian). Kompas . Retrieved 23 December 2021.
  11. ↑ Aisyah Llewellyn (14 December 2021). "Powerful undersea quake triggers panic in Indonesia". Al Jazeera . Retrieved 23 December 2021.
  12. ↑ Edna Tarigan (14 December 2021). "Indonesia lifts tsunami alert after powerful undersea quake". ABC News. Associated Press . Retrieved 23 December 2021.
  13. ↑ Dewi Nurita (14 December 2021). Aditya Budiman (ed.). "BMKG Cabut Peringatan Dini Tsunami di Gempa NTT" (in Indonesian). Tempo. Retrieved 23 December 2021.
  14. ↑ Achmad F. N. Sarjan; Zulfakriza Zulfakriza; Andri D. Nugraha; Shindy Rosalia; Shengji Wei; Sri Widiyantoro; Phil R. Cummins; Muzli Muzl; David P. Sahara; Nanang T. Puspito; Awali Priyono; Haunan Afif (22 April 2021). Basilios, Tsikouras (ed.). "Delineation of Upper Crustal Structure Beneath the Island of Lombok, Indonesia, Using Ambient Seismic Noise Tomography" (PDF). Frontiers in Earth Science. 9: 269. Bibcode:2021FrEaS...9..269S. doi: 10.3389/feart.2021.560428 . Retrieved 16 October 2021.
  15. 1 2 "Apa Penyebab Gempa di Laut Flores? Ini Penjelasan BMKG dan BRIN" (in Indonesian). Republika Online. Antara . Retrieved 23 December 2021.
  16. ↑ "M 7.8 - 37 km WNW of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey . Retrieved 23 December 2021.
  17. ↑ Yudho Winarto, ed. (17 December 2021). "BNPB: 5.064 Warga Mengungsi, 736 Rumah Rusak Akibat Gempa Flores" (in Indonesian). Kontan . Retrieved 23 December 2021.
  18. ↑ Firdaus, Fahmi (14 December 2021). "Update Gempa M,7,4: 230 Rumah dan Tempat Ibadah Rusak Berat di Kepulauan Selayar" (in Indonesian). Okezone. Retrieved 14 December 2021.
  19. ↑ Myesha Aqueena (16 December 2021). "Gempa Flores NTT Membuat 3.900 Orang Jadi Pengungsi, 9 Kabupaten Turut Merasakan Dampaknya" (in Indonesian). Jakpus News. Retrieved 23 December 2021.
  20. ↑ "Satu Korban Gempa Magnitudo 7,4 Kepulauan Selayar Meninggal Dunia". Republika (in Indonesian). 23 December 2021. Retrieved 4 April 2023.
  21. ↑ Kodrat Setiawan, ed. (16 December 2021). "3.900 Warga Selayar Mengungsi Akibat Gempa Flores" (in Indonesian). Tempo. Antara . Retrieved 23 December 2021.
  22. ↑ "346 Rumah Warga Selayar Rusak Akibat Gempa NTT". Cnnindonesia.com (in Indonesian). 15 December 2021. Retrieved 15 December 2021.
  23. ↑ "Indonesian quake rattles residents but only one hurt and minor damage". reuters.com. 14 December 2021. Retrieved 14 December 2021.
  24. ↑ "Sempat Dirawat, Warga Kepulauan Selayar Korban Gempa M7,4 Meninggal Dunia". okezone news (in Indonesian). 23 December 2021. Retrieved 23 December 2021.
  25. ↑ "Dampak Gempa M 7,4: Bangunan Rusak di Sulsel, 1 Orang Luka Ringan di Sikka". news detik.com (in Indonesian). 14 December 2021. Retrieved 14 December 2021.
  26. ↑ "Indonesians flee homes after 7.3 magnitude earthquake off Flores Island; tsunami warning lifted". South China Morning Post. Associated Press. 14 December 2021. Retrieved 24 December 2021.
  27. ↑ Eva Safitri (20 December 2021). "16 Ribu Lebih Warga Masih Ngungsi Karena Cemas Gempa Susulan di Selayar" (in Indonesian). Detik News. Retrieved 24 December 2021.
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