How Philippine Trench triggered magnitude 7.4 earthquake in Davao Oriental

The state seismologists pointed out that the magnitude 7.4 earthquake that struck offshore Manay, Davao Oriental on Friday morning was due to the movement of the Philippine Trench.

So what is the Philippine Trench and where is it located? 

The Philippine Trench is an oceanic trench, or long, narrow depressions on the oceanfloor. These are also the deepest parts of the ocean. According to the National Geographic, trenches were formed as a result of tectonic movements such as earthquakes or volcanic eruptions. 

The Philippine Trench is located in the eastern portion of the Philippines, spanning from Bicol in Luzon up to Mindanao, said Phivolcs director Teresito Bacolcol. 

Phivolcs explained that the earthquake occurred as a result of the Philippine Sea Plate pushing against and sliding beneath the Philippine Trench under the country’s archipelago. 

“So yung Philippine Sea Plate gumigitgit siya sa Philippine Trench doon sa under the Philippine Archipelago. So yung sea floor natin bends and dives under the Philippine Archipelago,” Bacolcol told GMA News Online in an interview. 

(So the Philippine Sea Plate is pushing against the Philippine Trench beneath the Philippine Archipelago. So our seafloor bends and dives under the Philippine Archipelago.) 

This movement causes friction, and sometimes the plates get stuck. 

“So may friction ‘yan. So minsan nagi-stuck. Yung Philippine Sea Plate kasi nagmo-move ‘yan towards the northwest. Kapag nagkakaroon po ng stress build-up, so kapag na-overcome ng Philippine Sea Plate yung friction, mag-slide down siya immediately at ‘yun yung lindol natin,” Bacolcol added. 

(So there’s friction. So sometimes it gets stuck. The Philippine Sea Plate moves towards the northwest. When stress build-up occurs, so when the Philippine Sea Plate overcomes the friction, it will slide down immediately, and that is our earthquake.) 

The Philippine Trench, which is one of the deepest in the world, is one of the six trenches in the country. The other trenches are: Manila Trench, Negros Trench, Sulu Trench, Cotabato Trench, and the East Luzon Trough. 

This is not the first time that the movement of the Philippine Trench caused an earthquake. In 2023, an offshore magnitude 7.4 earthquake also struck Hinatuan, Surigao del Sur. 

Phivolcs said that the movement in trenches is unpredictable. 

“Unpredictable din ‘yan. Parang lindol din ‘yan hindi natin  alam kung kailan gagalaw,” said Bacolcol. 

(That is also unpredictable. It’s also like an earthquake; we don't know when it will move.) 

The PHIVOLCS said last year that earthquakes as strong as magnitude 8, which can also cause tsunamis as high as 10 meters.

The Davao Oriental earthquake has killed at least one person and prompted the PHIVOLCS to raise a tsunami alert over seven areas. Phivolcs earlier lifted the tsunami warning at 1:43 p.m. –NB, GMA Integrated News