The 1976 Moro Gulf earthquake and tsunami occurred on August 17, 1976, at 00:11 local time near the islands of Mindanao and Sulu, in the Philippines. It measured 8.0 on the moment magnitude scale occurring at a depth of 20 km (12 mi).[2] The earthquake was accompanied by a destructive tsunami that resulted in a majority of the estimated 5,000 to 8,000 fatalities. It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake.
Several fault zones in the region are capable of producing major earthquakes and destructive local tsunamis. The two major fault zones that are most dangerous are the Sulu Trench in the Sulu Sea and the Cotabato Trench, a region of subduction that crosses the Celebes Sea and the Moro Gulf in Southern Mindanao. According to the PHIVOLCS historical catalog of earthquakes for the last 100 years, this region of the southern Philippines is characterized by moderate to high seismicity. The most recent earthquake along the Cotabato Trench region of subduction being the March 6, 2002, earthquake in Southern Mindanao.[citation needed]
Earthquakeedit
The earthquake occurred in an region where typical seismicity originates at 500 km (310 mi) depth on the Wadati–Benioff zones associated with subduction along the Sangihe and Mindanao islands. The Philippines is characterised by several complex and active subduction zones. The most geologically dominant in the region is the Philippine Trench located east of Mindanao. It dips to the west as represented by the Wadati–Benioff zone which can be detected to at least 200 km (120 mi).[3][4]
The mainshock had a shallow focal depth and represented thrust faulting along a plane dipping northeast at a shallow angle. The shock in the North Celebes Sea was associated with the smaller Cotabato Trench; a north–south bathymetric feature along the island's coast where it meets the Moro Gulf. Geologists have interpreted the earthquake as evidence for east–northeast-dipping subduction beneath Mindanao. The feature is also thought to be geologically young due to the absence of an active volcanic arc. In 1918, a major earthquake and tsunami ruptured a segment of the subduction zone south of the 1976 earthquake; both earthquakes ruptured a combined 300 km (190 mi) of the trench. The rupture propagated northward from the epicenter along the Cotabato Trench, evident from the aftershock zone. However, the strongest aftershock, measuring Ms 6.8, was the result of strike-slip faulting and occurred away from the aftershock zone.[3][4]
Near the Cotabato Trench, two of the largest 20th century Philippine earthquakes: the 1918 Celebes Sea earthquake (8.3 Mw) and the 1976 Moro Gulf earthquake (8.0 Mw). Also included is the 2002 Mindanao earthquake (7.5 Mw). The Moro Gulf, part of the Celebes Sea, is labeled for context.
The maximum height of the waves reached 9 meters at Lebak on the isla; 4.3 meters at Alicia; 3 meters at Resa Bay on the eastern coast of Basilan; and at the islands of Jolo and Sacol.[5] At least 5,000 people died during the earthquake and tsunami, with thousands more remaining missing.[6] Some reports say that as many as 8,000 people lost their lives in total, with ninety percent of all deaths the result of the following tsunami.
Initially over 8,000 people were officially counted as killed or missing, 10,000 injured, and 90,000 homeless, making it one of the most devastating disasters in the history of the Philippine Islands.[7] After the initial earthquake the people were unaware of the need to move to higher ground; when the tsunami hit it sucked most of the victims out to sea.[7] Based on the investigation on the affected region it was confirmed that the waves reached up to 4 to 5 metres (13 to 16 ft) when they hit the areas. There were reports of weak tsunami activity as far as Japan.[7]
In Zamboanga City, 14 buildings were partially damaged. The city was spared from serious damage of the tsunami triggered by this earthquake because the Basilan Island and the Santa Cruz Islands served as a buffer and deflected waves.[8]
^Engdahl, E. R.; Vallaseñor, A. (2002). "Global seismicity: 1900–1999" (PDF). International Handbook of Earthquake & Engineering Seismology. Part A, Volume 81A (First ed.). Academic Press. p. 683. ISBN978-0124406520.
^ abStewart, Gordon S.; Cohn, Stephen N. (1979). "The 1976 August 16, Mindanao, Philippine earthquake (Ms = 7.8) - evidence for a subduction zone south of Mindanao". Geophysical Journal International. 57 (1): 51–65. Bibcode:1979GeoJ...57...51S. doi:10.1111/j.1365-246X.1979.tb03771.x.
^ abBeck, Susan L.; Ruff, Larry. J. (1985). "The rupture process of the 1976 Mindanao Earthquake". Journal of Geophysical Research: Solid Earth. 90 (B8): 6773–6782. Bibcode:1985JGR....90.6773B. doi:10.1029/JB090iB08p06773.
^Department, Commerce; Dunbar, Paula K. (April 24, 2015). Pacific Tsunami Warning System: A Half Century of Protecting the Pacific, 1965–2015. Government Printing Office. pp. 46–47. ISBN978-0-9962579-0-9. Retrieved August 22, 2017.
^ abcStaff of the Academy of Sciences of the USS (1997). Catalog of Tsunamis in the Pacific 1969–1982. Diane Pub. pp. 103, 104. ISBN978-0-7881393-1-4.
^. Philippine Institute of Volcanology and Seismology. Archived from the original on October 15, 2013. Retrieved October 15, 2013.
^Philippine Institute of Volcanology and Seismology (2018). "PHIVOLCS Earthquake Intensity Scale (PEIS)". Retrieved November 13, 2019.
External linksedit
Philippines Institute of Volcanology and Seismology January 29, 2010, at the Wayback Machine
The Earthquake and Tsunami of August 16, 1976, in the Philippines – The Moro Gulf Tsunami" – George Pararas-Carayannis
The International Seismological Centre has a bibliography and/or authoritative data for this event.
January 19, 2024
1976, moro, gulf, earthquake, tsunami, occurred, august, 1976, local, time, near, islands, mindanao, sulu, philippines, measured, moment, magnitude, scale, occurring, depth, earthquake, accompanied, destructive, tsunami, that, resulted, majority, estimated, fa. The 1976 Moro Gulf earthquake and tsunami occurred on August 17 1976 at 00 11 local time near the islands of Mindanao and Sulu in the Philippines It measured 8 0 on the moment magnitude scale occurring at a depth of 20 km 12 mi 2 The earthquake was accompanied by a destructive tsunami that resulted in a majority of the estimated 5 000 to 8 000 fatalities It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake 1976 Moro Gulf earthquake and TsunamiTsunami damage at Lebak MindanaoUTC time1976 08 16 16 11 08ISC event709878USGS ANSSComCatLocal dateAugust 17 1976 1976 08 17 Local time00 11 07Magnitude8 0 MwDepth20 km 12 mi Epicenter6 17 N 124 05 E 6 29 N 124 09 E 6 29 124 09 1 TypeMegathrustAreas affectedPhilippinesMax intensityVIII Severe PEIS VII Destructive Tsunami4 5 m 13 16 ft Casualties5 000 8 000 dead 10 000 injured 90 000 homeless Contents 1 Tectonic summary 2 Earthquake 3 Impact 4 See also 5 References 6 External linksTectonic summary edit nbsp Tsunami damage at barangay Tibpuan Lebak MindanaoSeveral fault zones in the region are capable of producing major earthquakes and destructive local tsunamis The two major fault zones that are most dangerous are the Sulu Trench in the Sulu Sea and the Cotabato Trench a region of subduction that crosses the Celebes Sea and the Moro Gulf in Southern Mindanao According to the PHIVOLCS historical catalog of earthquakes for the last 100 years this region of the southern Philippines is characterized by moderate to high seismicity The most recent earthquake along the Cotabato Trench region of subduction being the March 6 2002 earthquake in Southern Mindanao citation needed Earthquake editThe earthquake occurred in an region where typical seismicity originates at 500 km 310 mi depth on the Wadati Benioff zones associated with subduction along the Sangihe and Mindanao islands The Philippines is characterised by several complex and active subduction zones The most geologically dominant in the region is the Philippine Trench located east of Mindanao It dips to the west as represented by the Wadati Benioff zone which can be detected to at least 200 km 120 mi 3 4 The mainshock had a shallow focal depth and represented thrust faulting along a plane dipping northeast at a shallow angle The shock in the North Celebes Sea was associated with the smaller Cotabato Trench a north south bathymetric feature along the island s coast where it meets the Moro Gulf Geologists have interpreted the earthquake as evidence for east northeast dipping subduction beneath Mindanao The feature is also thought to be geologically young due to the absence of an active volcanic arc In 1918 a major earthquake and tsunami ruptured a segment of the subduction zone south of the 1976 earthquake both earthquakes ruptured a combined 300 km 190 mi of the trench The rupture propagated northward from the epicenter along the Cotabato Trench evident from the aftershock zone However the strongest aftershock measuring Ms 6 8 was the result of strike slip faulting and occurred away from the aftershock zone 3 4 Impact edit nbsp The Cotabato Trench in southern Mindanao and the Philippine Mobile Belt nbsp nbsp Moro Gulf nbsp 1976 nbsp 1918 nbsp 2002class notpageimage Near the Cotabato Trench two of the largest 20th century Philippine earthquakes the 1918 Celebes Sea earthquake 8 3 Mw and the 1976 Moro Gulf earthquake 8 0 Mw Also included is the 2002 Mindanao earthquake 7 5 Mw The Moro Gulf part of the Celebes Sea is labeled for context The initial earthquake was widespread and was felt as far as the central Philippine islands of the Visayas A massive tsunami devastated 700 kilometers of coastline bordering the Moro Gulf in the North Celebes Sea resulting in destruction and death in the coastal communities of the Sulu Archipelago southern Mindanao particularly the provinces of Sultan Kudarat and Sarangani formerly part of South Cotabato and in the Zamboanga Peninsula including Zamboanga City and Pagadian City citation needed The maximum height of the waves reached 9 meters at Lebak on the isla 4 3 meters at Alicia 3 meters at Resa Bay on the eastern coast of Basilan and at the islands of Jolo and Sacol 5 At least 5 000 people died during the earthquake and tsunami with thousands more remaining missing 6 Some reports say that as many as 8 000 people lost their lives in total with ninety percent of all deaths the result of the following tsunami Initially over 8 000 people were officially counted as killed or missing 10 000 injured and 90 000 homeless making it one of the most devastating disasters in the history of the Philippine Islands 7 After the initial earthquake the people were unaware of the need to move to higher ground when the tsunami hit it sucked most of the victims out to sea 7 Based on the investigation on the affected region it was confirmed that the waves reached up to 4 to 5 metres 13 to 16 ft when they hit the areas There were reports of weak tsunami activity as far as Japan 7 In Zamboanga City 14 buildings were partially damaged The city was spared from serious damage of the tsunami triggered by this earthquake because the Basilan Island and the Santa Cruz Islands served as a buffer and deflected waves 8 Intensity distribution by location 9 Intensity scales LocationVII Cotabato City Jolo Sulu Zamboanga CityVI Basilan City Pagadian City Dipolog City Malaybalay BukidnonV Cagayan de Oro City Davao City General SantosIV Dumaguete Hinatuan Surigao del Sur Tagbilaran Bohol Cebu City Surigao Surigao del NorteII Roxas City Iloilo City Tacloban City Legaspi City Palo Leyte Catbalogan SamarSee also editList of earthquakes in 1976 List of earthquakes in the PhilippinesReferences edit Engdahl E R Vallasenor A 2002 Global seismicity 1900 1999 PDF International Handbook of Earthquake amp Engineering Seismology Part A Volume 81A First ed Academic Press p 683 ISBN 978 0124406520 ISC 2022 ISC GEM Global Instrumental Earthquake Catalogue 1904 2018 Version 9 1 International Seismological Centre a b Stewart Gordon S Cohn Stephen N 1979 The 1976 August 16 Mindanao Philippine earthquake Ms 7 8 evidence for a subduction zone south of Mindanao Geophysical Journal International 57 1 51 65 Bibcode 1979GeoJ 57 51S doi 10 1111 j 1365 246X 1979 tb03771 x a b Beck Susan L Ruff Larry J 1985 The rupture process of the 1976 Mindanao Earthquake Journal of Geophysical Research Solid Earth 90 B8 6773 6782 Bibcode 1985JGR 90 6773B doi 10 1029 JB090iB08p06773 Department Commerce Dunbar Paula K April 24 2015 Pacific Tsunami Warning System A Half Century of Protecting the Pacific 1965 2015 Government Printing Office pp 46 47 ISBN 978 0 9962579 0 9 Retrieved August 22 2017 History of Tsunami Devastation a b c Staff of the Academy of Sciences of the USS 1997 Catalog of Tsunamis in the Pacific 1969 1982 Diane Pub pp 103 104 ISBN 978 0 7881393 1 4 Moro Gulf Earthquake 17 August 1976 Philippine Institute of Volcanology and Seismology Archived from the original on October 15 2013 Retrieved October 15 2013 Philippine Institute of Volcanology and Seismology 2018 PHIVOLCS Earthquake Intensity Scale PEIS Retrieved November 13 2019 External links editPhilippines Institute of Volcanology and Seismology Archived January 29 2010 at the Wayback Machine The Earthquake and Tsunami of August 16 1976 in the Philippines The Moro Gulf Tsunami George Pararas Carayannis The International Seismological Centre has a bibliography and or authoritative data for this event Retrieved from https en wikipedia org w index php title 1976 Moro Gulf earthquake amp oldid 1190147941, wikipedia, wiki, book, books, library,
