2021 Flores earthquake

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2021 Flores earthquake
2021-12-14 Flores Sea M7.3 earthquake shakemap (USGS).jpg
2021 Flores earthquake is located in Indonesia
2021 Flores earthquake
UTC time2021-12-14 03:20:24
ISC event621629136
USGS-ANSSComCat
Local dateDecember 14, 2021 (2021-12-14)
Local time11:20:24 WITA
Magnitude7.3 Mw
Depth16.1 km (10.0 mi)
Epicenter7°36′11″S 122°12′00″E / 7.603°S 122.200°E / -7.603; 122.200Coordinates: 7°36′11″S 122°12′00″E / 7.603°S 122.200°E / -7.603; 122.200[1]
Areas affectedIndonesia
Total damageModerate
Max. intensityV (Moderate)
Tsunami7 cm (2.8 in)
Aftershocks896 (as of Dec 20, 2021)
Casualties1 dead, 97 injured

The 2021 Flores earthquake occurred 112 km, offshore, north of Maumere in the Flores Sea on December 14.[1] The moment magnitude (Mw) of 7.3 according to the United States Geological Survey (USGS), occurred just a few days after the anniversary of another quake in the same region; the 1992 Flores earthquake. One person was killed and 97 others suffered injuries.

Earthquake[]

Initially a magnitude 7.7, it was downgraded to 7.3.[2] The quake was the result of shallow strike-slip faulting within the shallow crust beneath the Flores Sea. According to the U.S. Geological Survey (ANSS), the earthquake rupture was on an east northeast-west southwest fault with a right-lateral strike-slip motion.

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.[3]

Scientists at the 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.[4]

The shaking was reportedly most intense on the Selayar Islands, reaching a maximum Modified Mercalli intensity of V (Moderate) acording to the Meteorology, Climatology, and Geophysical Agency (BMKG). The ANSS ShakeMap simulation revealed a maximum intensity of V (Moderate). The earthquake was also felt V in Ranakah.[5] In Lembata, Labuan Bajo, Larantuka and Ruteng, weak shaking (III-IV) was felt.[6]

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.[7] The tsunami however, was minor, measuring only 7 centimeters (2.8 inches).[8] Warnings were cancelled two hours later at 13:20 local time.[9]

Tectonic setting[]

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.[10]

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.[11] The earthquake was the largest in the region since a deep-focus Mw  7.9 struck in 1996.[12]

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, Flores Back Arc Thrust Fault was responsible for the magnitude 7.8 earthquake in 1992 that triggered a devastating tsunami, as well as the 2018 Lombok earthquakes.[13][14]

Impact[]

Hundreds of residents were displaced in Selayar Islands due to the quake

The Selayar and Flores islands were affected by the earthquake; at least 830 homes were destroyed and 1,249 were damaged,[15] and 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.[16] Three school buildings, two mosques, two places of worship and a village office were also damaged.[17] Damage to buildings included roof collapse, toppled concrete walls of fence and homes and collapse of entire homes.[18]

A total of 97 people had minor injuries,[19] and one whose injuries were severe.[20] Some were injured when falling in a panic caused by the tsunami warning system.[21][22][23] On December 23, the elderly man with severe head injuries after being hit by falling debris died at the hospital while receiving treatment.[24] At least one of the injured was from East Nusa Tenggara while the rest were in South Sulawesi.[25]

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.[13]

By December 20, 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.[26]

See also[]

References[]

  1. ^ a b c "M 7.3 - 112 km N of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey. 14 December 2021. Retrieved 14 December 2021.
  2. ^ "Magnitude 7.7 earthquake strikes near Maumere, East Nusa Tenggara". The Jakarta Post. 14 December 2021. Retrieved 23 December 2021.
  3. ^ Ahmad Arif (16 December 2021). "Gempa yang Mengingatkan Tsunami Flores 1992" (in Indonesian). Kompas. Retrieved 23 December 2021.
  4. ^ Lauriane Chardot (16 December 2021). "The Mw 7.3 Earthquake Off the Coast of Flores Likely Occurred on a Known Fault". earthobservatory.sg. . Retrieved 23 December 2021.
  5. ^ "Earthquake and tsunami". magma.esdm.go.id (in Indonesian). MAGMA Indonesia. 16 December 2021. Retrieved 23 December 2021.
  6. ^ 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.
  7. ^ Aisyah Llewellyn (14 December 2021). "Powerful undersea quake triggers panic in Indonesia". Al Jazeera. Retrieved 23 December 2021.
  8. ^ Edna Tarigan (14 December 2021). "Indonesia lifts tsunami alert after powerful undersea quake". ABC News. Associated Press. Retrieved 23 December 2021.
  9. ^ Dewi Nurita (14 December 2021). Aditya Budiman (ed.). "BMKG Cabut Peringatan Dini Tsunami di Gempa NTT" (in Indonesian). Tempo. Retrieved 23 December 2021.
  10. ^ 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. doi:10.3389/feart.2021.560428. Retrieved 16 October 2021.
  11. ^ Daryono Daryono (21 December 2021). Shierine Wangsa Wibawa (ed.). "Mengenali Jalur Sesar Pembangkit Gempa Laut Flores" (in Indonesian). Kompas. Retrieved 23 December 2021.
  12. ^ "M 7.9 - 112 km NNE of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey. 17 June 1996. Retrieved 24 January 2022.
  13. ^ a b "Apa Penyebab Gempa di Laut Flores? Ini Penjelasan BMKG dan BRIN" (in Indonesian). Republika Online. Antara. Retrieved 23 December 2021.
  14. ^ "M 7.8 - 37 km WNW of Maumere, Indonesia". earthquake.usgs.gov. U.S. Geological Survey. Retrieved 23 December 2021.
  15. ^ "Risklayer Explorer". risklayer.com.
  16. ^ Yudho Winarto, ed. (17 December 2021). "BNPB: 5.064 Warga Mengungsi, 736 Rumah Rusak Akibat Gempa Flores" (in Indonesian). Kontan. Retrieved 23 December 2021.
  17. ^ 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.
  18. ^ 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.
  19. ^ Muhammad Refi Sandi (17 December 2021). "BNPB: 5.064 Warga Mengungsi, 736 Rumah Rusak Akibat Gempa Flores" (in Indonesian). SINDOnews. Retrieved 23 December 2021.
  20. ^ Kodrat Setiawan, ed. (16 December 2021). "3.900 Warga Selayar Mengungsi Akibat Gempa Flores" (in Indonesian). Tempo. Antara. Retrieved 23 December 2021.
  21. ^ "346 Rumah Warga Selayar Rusak Akibat Gempa NTT". Cnnindonesia.com (in Indonesian). 15 December 2021. Retrieved 15 December 2021.
  22. ^ "Indonesian quake rattles residents but only one hurt and minor damage". reuters.com. 14 December 2021. Retrieved 14 December 2021.
  23. ^ "Sempat Dirawat, Warga Kepulauan Selayar Korban Gempa M7,4 Meninggal Dunia". okezone news (in Indonesian). 23 December 2021. Retrieved 23 December 2021.
  24. ^ "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.
  25. ^ "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.
  26. ^ 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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