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1980 Azores Islands earthquake

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1980 Azores Islands
1980 Azores Islands earthquake is located in Azores
1980 Azores Islands earthquake
Terceira
Terceira
Graciosa
Graciosa
São Jorge
São Jorge
UTC time1980-01-01 16:42:42
ISC event652123
USGS-ANSSComCat
Local date1 January 1980 (1980-01-01)
Local time15:42:42
Magnitude6.9 Mw(ISC-GEM) 
Depth10 kilometres (6 mi)
Epicenter50 km west of Angra do Heroísmo
38°49′N 27°47′W / 38.81°N 27.78°W / 38.81; -27.78
TypeStrike-slip
Areas affectedPortugal
Azores
Max. intensityMMI VIII (Severe)–MMI IX (Violent)[1]
TsunamiA small tsunami was registered in Angra do Heroismo
Casualties73 dead, 400 injured

Striking the Autonomous Region of the Azores on 1 January, the 1980 Azores Island earthquake killed 73 people and injured over 400, causing severe damage on the islands of Terceira and São Jorge. Resulting from a strike slip fracture, typical of other historical Azorean earthquakes, and measuring 6.9 on the moment magnitude scale, it also shook the islands of Pico and Faial.

In response to the earthquake, Portuguese president António Ramalho Eanes announced three days of national mourning, while relief efforts, initiated by agents of the local Air Force, were soon accompanied by government-supported agencies.

Geology

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Background

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In 1950, another strong earthquake had rocked the Azores Islands region, and this was the largest earthquake since.[2]

Description

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Volcanic in origin, the Azores lie in a tectonically complex area on either side of the Mid-Atlantic Ridge, between the European, American and African plate boundaries, forming their own microplate.[3] The 1980 earthquake was the result of movement along a northwest to southeast trending strike-slip fault.[3]

After aftershocks from the quake had concluded, a study took place, identifying focal solutions for these small events. The type of faulting responsible for these shocks was similar to that of previous earthquakes around the Azores. For these earthquakes, scientists had determined that the conjugate nodal plane was responsible, seeing shearing in the right-lateral (dextral) direction.[4] All faulting in this area is strike-slip-oriented, and on a rather large scale.[5] Because of this research, information now points towards Azores volcanism being controlled by earthquake movement.[4]

Damage and casualties

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The earthquake that struck the Azorean islands was 6.9 Mw. It caused considerable damage on three separate islands (Terceira, São Jorge Island, and Graciosa),[6] destroying several buildings.[7] According to local reports, roughly 70% of the houses on Terceira were completely demolished, including the historic quarter of the island capital, Angra do Heroísmo.[2] In general, public buildings such as churches remained intact, while several buildings caved in on themselves.[2] Public utilities such as electricity and water, were reported cut in several areas.[2]

Initially, the number of fatalities was set at 52.[7] It was later revised to 61 and finally to 72.[3][8][9] Additionally, the injuries were set at 300,[10] but this was also revised to more than 400.[6] At least 20,000 people were left homeless.[11] Minor damage was recorded at Pico and Faial islands.[2]

No fatalities were recorded at the Lajes Field air base, nor any major damage.[2]

Relief efforts and response

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United States Navy and Air Force personnel stationed at Lajes functioned as disaster relief workers,[2] sheltering as many as 150 families.[12] Portuguese Air Force members brought supplies to earthquake victims, while a Portuguese Navy João Coutinho-class corvette transported medical officials to the island. The Portuguese president, António Ramalho Eanes, flew in on a plane accompanied by medical personnel and supplies (such as bedding).[2] Local officials including policemen and volunteer firemen cleared roads for relief supplies and transports. Responding to the situation, these officials were also involved in looking for survivors in the rubble.[2] Soon after, tents were erected to replace the destroyed or unsafe homes for approximately 200 families of the islands. Portable homes were constructed by the People to People International project fund, resulting in 100 shelters.[12]

Three days of national mourning were declared by Eanes.[2] Following the relief efforts, 19 seismographic stations were installed to monitor seismic activities. Eleven of these were used to monitor earthquake activity, while the other eight also record information on the island's geothermal areas.[13]

The earthquake forced hundreds of people to leave the country for the United States. It occurred during a period of several major natural disasters in which many residents of the island left; in 1975, 8,000 residents left. In 1981, however, just 2,500 people left the island.[11]

Analysis and current situation

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Later studies of the events leading up to the tragedy found several factors contributing to the extent of the damage. A. Malheiro (2006) linked five major causes to damage from these earthquakes. The buildings most damaged by the earthquake were near fault lines on top of loosely packed soil. They tended to be of poor construction and did not conform to proper building code, nor had they been adequately examined.[14]

The area around the Azores remains active. Threats from earthquakes and landslides remain.[14]

See also

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References

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Notes
  1. ^ "Significant Earthquake: AZORES: TERCEIRA, ANGRA DO HEROISMO". National Geophysical Data Center. 1 January 1980. Retrieved 23 June 2021.
  2. ^ a b c d e f g h i j Western Newspapers (2 January 1980)
  3. ^ a b c Borges et al. (2007), p.37–54
  4. ^ a b Hirn, A.; Haessler, H.; Trong, P. Hoang; Wittlinger, G.; Victor, L. A. Mendes (July 1980). "Aftershock sequence of the January 1, 1980, earthquake and present-day tectonics in the Azores". Geophysical Research Letters. 7 (7): 501–504. Bibcode:1980GeoRL...7..501H. doi:10.1029/GL007i007p00501.
  5. ^ Udías, Agustín; Buforn, Elisa (1990). "Regional stresses along the Eurasia-Africa plate boundary derived from focal mechanisms of large earthquakes". Pure and Applied Geophysics. 136 (4): 433–448. Bibcode:1991PApGe.136..433U. doi:10.1007/BF00878580. S2CID 129343125.
  6. ^ a b "Today in Earthquake History: January 1". United States Geological Survey. 18 February 2009. Archived from the original on 1 June 2008. Retrieved 1 September 2009.
  7. ^ a b "Quake Hits Azores Islands; at Least 52 Die, 300 Hurt". Los Angeles Times. 2 January 1980. Archived from the original on 22 October 2012. Retrieved 1 September 2009.
  8. ^ Ferreira, Marta Leite. "Sismo dos Açores em 1980. A história do terramoto mais destrutivo dos últimos 200 anos em Portugal". Observador (in European Portuguese). Retrieved 18 April 2024.
  9. ^ Mendes, Ana Isabel (8 March 2014). "Memórias do sismo de 1980 nos Açores reunidas num "site"". PÚBLICO (in Portuguese). Retrieved 18 April 2024.
  10. ^ "Earthquake Kills 52 in the Azores". The New York Times. 2 January 1980. Retrieved 1 September 2009.
  11. ^ a b "Azores' Exiles Forsake U.S. And Go Home". The New York Times. 3 October 1982.
  12. ^ a b "Lajes Field History – Humanitarian Efforts, 1980s and 1990s". Lajes Air Field. Archived from the original on 7 May 2008. Retrieved 19 September 2009.
  13. ^ Lee & Hung 2003, p. 1415.
  14. ^ a b Malheiro, A. (August 2006). "Geological hazards in the Azores archipelago: Volcanic terrain instability and human vulnerability". Journal of Volcanology and Geothermal Research. 156 (1–2): 158. Bibcode:2006JVGR..156..158M. doi:10.1016/j.jvolgeores.2006.03.012.
Sources
  • Lee, Kan; Hung, William (2003). International handbook of earthquake and engineering seismology, Part 2. International Association of Seismology and Physics of the Earth's Interior's.
  • Silva, M (2005). Caracterização da sismicidade histórica dos Açores com base na reinterpretação de dados de macrossísmica: contribuição para avaliação do risco sísmico nas ilhas do Grupo Central (in Portuguese). Ponta Delgada: University of the Azores, Departamento de Geociências. p. 146.
  • Madeira, J.; A. Ribeiro (1992). "O regime tectónico nos Açores". In C.S. Oliveira; A.R. Lucas; J.H. Guedes (eds.). Monografia 10 anos após o sismo dos Açores de 1 de Janeiro de 1980 (in Portuguese). Vol. 1. Secretaria Regional da Habitação e Obras Públicas (Terceira); Laboratório Nacional de Engenharia Civil (Lisbon). pp. 163–174.
  • CVARG (2010). "Sismo de 1 de Janeiro de 1980". Centro de Vulcanologia e Availação de Riscos Geológicos. Archived from the original on 5 March 2012. Retrieved 9 April 2010.
  • Borges, J.F.; Bezzeghoud, M.; Buforn, E.; Pro, C.; Fitas, A. (2007), "The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications", Tectonophysics, 435 (1–4): 37–54, Bibcode:2007Tectp.435...37B, doi:10.1016/j.tecto.2007.01.008, hdl:10174/6383
  • Udías, Agustín; Buforn, Elisa (1990). "Regional stresses along the Eurasia-Africa plate boundary derived from focal mechanisms of large earthquakes". Pure and Applied Geophysics. 136 (4). Birkhäuser Basel: 433–448. Bibcode:1991PApGe.136..433U. doi:10.1007/BF00878580. S2CID 129343125.
  • "Earthquakes devastates Azores Island". Western Newspapers Inc. 2 January 1980. Retrieved 1 September 2009.
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