1976 Moro Gulf earthquake

The 1976 Moro Gulf earthquake and tsunami took place on August 17, 1976, at 00:11 local time near the islands of Mindanao and Sulu, in the Philippines. Its magnitude was calculated as being as high as 8.0 on the moment magnitude scale.

1976 Moro Gulf earthquake and Tsunami
Tsunami damage at Lebak, Mindanao
1976 Moro Gulf earthquake is located in Mindanao
1976 Moro Gulf earthquake
1976 Moro Gulf earthquake is located in Philippines
1976 Moro Gulf earthquake
UTC time1976-08-16 16:11:08
ISC event709878
USGS-ANSSComCat
Local dateAugust 17, 1976 (1976-08-17)
Local time00:11:07
Magnitude8.0 Mw[1]
Depth59 km (37 mi)[1]
Epicenter6.29°N 124.09°E / 6.29; 124.09[1]
TypeMegathrust
Areas affectedPhilippines
Max. intensity
[2]
Tsunami4–5 m (13–16 ft)
Casualties5,000–8,000 killed
10,000 injured
90,000 homeless

It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake.

Tectonic summary
Tsunami damage at barangay Tibpuan, Lebak, Mindanao

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.

Intensity Report
1976 Mw 8.0 Moro Gulf Earthquake[3]
Intensity

scales

 Location
VII Cotabato City; Jolo-Sulu; Zamboanga City
VI Basilan City; Pagadian City; Dipolog City; Malaybalay-Bukidnon
V Cagayan de Oro City; Davao City; General Santos
IV Dumaguete; Hinatuan Surigao del Sur; Tagbilaran-Bohol; Cebu City; Surigao-Surigao del Norte
II Roxas City; Iloilo City; Tacloban City; Legaspi City; Palo-Leyte; Catbalogan-Samar

Effects
The Cotabato Trench in southern Mindanao and the Philippine Mobile Belt.
Earthquakes in Mindanao
Moro Gulf
1976
1976
1918
1918
2002
2002
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.

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.[4] At least 5,000 people died during the earthquake and tsunami, with thousands more remaining missing.[5] 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.[6] 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.[6] 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.[6]

In Zamboanga City, 14 buildings were partially damaged. Zamboanga 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.[7]

See also

References
  1. 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. ISBN 978-0124406520.
  2. Philippine Institute of Volcanology and Seismology (2018). "PHIVOLCS Earthquake Intensity Scale (PEIS)". Retrieved November 13, 2019.
  3. Looking Back: What Filipinos learned from the 1976 Moro Gulf Earthquake? whatalife.ph
  4. 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.
  5. History of Tsunami Devastation
  6. 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.
  7. "Moro Gulf Earthquake – 17 August 1976". Philippine Institute of Volcanology and Seismology. Archived from the original on October 15, 2013. Retrieved October 15, 2013.
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