2021 Davao Oriental earthquake

Earthquake in the Philippines

6°18′N 126°52′E / 6.30°N 126.87°E / 6.30; 126.87FaultPhilippine TrenchAreas affectedMindanaoMax. intensityMMI VII (Very strong)
PEIS V (Strong)TsunamiYesForeshocks4.4 Mw AftershocksMultiple, Strongest - 5.7 Casualties1 dead

On August 12, 2021, at 01:46:12 PST, a strong Mw  7.1 earthquake struck the island of Mindanao at a depth of 55.1 kilometers (34.2 mi). It had a maximum perceived Intensity V on the PHIVOLCS Earthquake Intensity Scale.[1] No damage or injuries were reported but a young man was killed by the earthquake.

Tectonic setting

The Philippines islands were formed in evolutionary processes involving Subductions, and collisions. Earthquakes are frequent there as a result of collision processes between the Philippine Sea Plate (PSP) and the Sunda Plate (SP). The slip convergence between PSP and the SP boundary is obliquely accommodated by the Philippine fault system, which is a major left-lateral strike-slip fault system. The Philippine fault has been slipping at a rate of 33 ± 11 mm/yr in the northern and central Leyte sections. The southern part of the Philippine fault is mainly located in eastern Mindanao and constitutes a complex fault system with discrete strands and splays. Mindanao island is located on the complex collision boundary between the SP and the PSP. Some parts of the convergence between these plates are consumed by the Philippine fault and subduction at the Cotabato trench.

Earthquake

Modified Mercalli intensities in selected locations[2]
MMI Locations Population exposure
MMI VII (Very strong) Pondaguitan 276,000
MMI VI (Strong) Mati 806,000
MMI V (Moderate) Davao City 7.03 million
MMI IV (Light) Tandag 13.1 million

The earthquake struck near Davao Oriental early on Thursday morning, August 12. PHIVOLCS earlier listed the earthquake as magnitude 7.3 at a depth of 69 kilometers, then revised its advisory to a magnitude 7.2 earthquake, which occurred at a depth of 50 kilometers. It later reverted to its original report of a magnitude 7.3 earthquake. At 6:06 am, PHIVOLCS further revised its report to a magnitude 7.1 earthquake, at a depth of 39 km (kilometers). The United States Geological Survey also measured the quake at 7.1.

PHIVOLCS Reported Intensities[1]
Intensity

Scale

Location
V City of Mati, Baganga, Governor Generoso, and Lupon, Davao Oriental; City of Panabo, City of Tagum, and Carmen, Davao del Norte; Nabunturan,

Davao de Oro; City of General Santos; Alabel, and Malungon, Sarangani; Sarangani, Davao Occidental

IV City of Davao; Kiblawan, Davao del Sur; City of Koronadal, Banga, Polomolok, Tampakan, and Tupi, South Cotabato; Glan, Malapatan, and

Kiamba, Sarangani; Monkayo, Davao de Oro

III City of Kidapawan, and Kabacan, Cotabato; City of Bayugan, Agusan del Sur; Maasim, Sarangani; Norala, Surallah, Santo Niño, and T'boli, South

Cotabato

II City of Cagayan de Oro; City of Tacurong, and President Quirino, Sultan Kudarat; City of Bislig, and Hinatuan, Surigao del Sur; Talakag, Bukidnon;

Alamada, Antipas, Arakan, Banisilan, Magpet, and President Roxas, Cotabato

I Mambajao, Camiguin

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported in a bulletin that the earthquake, which was tectonic in origin, struck at 1:46 am off the coast of Davao Oriental. PHIVOLCS said that there was no tsunami threat but damage and aftershocks were expected.[3]

Local authorities have deployed personnel to assess structures for any damage and injuries following the earthquake.[4] In Davao City, workers of different businesses went out of their offices due to the earthquake.

Mindanao is regularly rocked by quakes due to its location on the Pacific "Ring of Fire".[5]

Aftershocks ranging in magnitude 4's and 5's followed after the mainshock early morning in Philippines. A moderately strong shallow aftershock was felt at midnight on August 12. The strongest aftershocks were reported magnitude 5.1 and 5.7 intensities of III.[6][7] The earthquake was felt mostly all over Mindanao and lasted for more than a minute.

Foreshock, Mainshock and Aftershocks of the August 2021 Davao Oriental earthquake (United States Geological Survey)[8]
Date Time (UST) Magnitude 5.0 ^ Mw  Intensity Depth Location Reference
August 11 9:44 AM 4.4 None 63.3 km 017 km S 05° W of Tarragona (Davao Oriental) [9]
August 12 1:46 AM 7.1 VII 57.7km 60 km ENE of Pondaguitan, Philippines [10]
August 12 10:26 AM 5.2 None 35km 125 km ESE of Pondaguitan, Philippines [11]
August 12 11:42 PM 5.1 III 35km 107 km ESE of Pondaguitan, Philippines [7]
August 12 11:53 PM 5.7 III 10km Philippine Islands region [6]
August 13 2:01 AM 5.0 None 10km 109 km E of Pondaguitan, Philippines [12]
August 13 4:17 AM 5.3 None 64km 111 km ESE of Pondaguitan, Philippines [13]
August 13 4:28 AM 5.3 None 35km 113 km ESE of Pondaguitan, Philippines [14]
August 13 5:03 AM 5.3 None 47km 114 km ESE of Pondaguitan, Philippines [15]
August 14 9:27 AM 5.1 None 53km 108 km ESE of Pondaguitan, Philippines [16]

Tsunami

A tsunami was generated with recorded wave heights of 6.1 cm at Bitung, Indonesia and 3 cm at Davao City, Philippines.[10]

Other events

An earthquake measuring a magnitude of 7.0 struck the same location on January 21, 2021. Despite the location, there is no evidence of a casual relationship between these two events due to the long period of time between them.

Damage and casualties

The Department of Transportation said there were only minor cracks on the runway of the airport in Mati, but no damage to the passenger terminal. There was no damage at Francisco Bangoy International Airport as well as port facilities and public terminals in the region, it added. [17] Despite that there is no damage reported. [18]

A 20-year-old man in Tandag died after being hit in the head by falling coconuts following the earthquake.[19]

See also

References

  1. ^ a b "Earthquake Information No. 4". Philippine Institute of Volcanology and Seismology. August 12, 2021. Retrieved September 3, 2021.
  2. ^ "PAGER". USGS. February 25, 2022. Archived (PDF) from the original on February 18, 2022. Retrieved February 25, 2022.
  3. ^ "Magnitude 7.1 earthquake strikes off Davao Oriental". Rappler. August 11, 2021. Retrieved September 1, 2021.
  4. ^ "Magnitude 7.1 quake hits waters off Davao Oriental". cnn. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  5. ^ "Magnitude 7.1 quake strikes off Davao Oriental". ABS-CBN News. August 11, 2021. Retrieved September 1, 2021.
  6. ^ a b "USGS". earthquake.usgs.gov. Archived from the original on August 12, 2021. Retrieved September 1, 2021.
  7. ^ a b "USGS". earthquake.usgs.gov. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  8. ^ "Latest Earthquakes". earthquake.usgs.gov. Retrieved August 28, 2021.
  9. ^ "USGS 4.4 Foreshock". earthquake.usgs.gov. Archived from the original on August 28, 2021. Retrieved August 28, 2021.
  10. ^ a b "USGS on August 2021 Mindanao Quake". earthquake.usgs.gov. Archived from the original on August 11, 2021. Retrieved August 28, 2021.
  11. ^ "USGS". earthquake.usgs.gov. Archived from the original on August 12, 2021. Retrieved August 28, 2021.
  12. ^ "USGS". earthquake.usgs.gov. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  13. ^ "USGS". earthquake.usgs.gov. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  14. ^ "USGS". earthquake.usgs.gov. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  15. ^ "USGS". earthquake.usgs.gov. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  16. ^ "USGS". earthquake.usgs.gov. Archived from the original on August 14, 2021. Retrieved September 1, 2021.
  17. ^ "Magnitude 7.1 quake hits waters off Davao Oriental". CNN Philippines. Archived from the original on September 1, 2021. Retrieved September 1, 2021.
  18. ^ Llemit, Ralph Lawrence G. (August 12, 2021). "No damage in Davao Oriental after 7.1-M earthquake". Sunstar. Retrieved September 1, 2021.
  19. ^ Alexander Lopez (August 13, 2021). "Fallen coconuts from strong quake kill man in Tandag City". Philippine News Agency. Retrieved September 3, 2021.
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  • † indicates earthquake resulting in at least 30 deaths
  • ‡ indicates the deadliest earthquake of the year
  • Dates for all earthquakes are in UTC