How major Philippine trenches shape earthquakes in the country

Neil Gregori Garen
Oct 28
2 min read

Have you ever wondered why earthquakes in the Philippines happen so frequently? Or what lies beneath our surrounding seas that makes our islands part of one of the most seismically active regions on Earth?

The Philippines sits right on the Pacific Ring of Fire, where several tectonic plates collide, dive, and grind past each other. This dynamic setup creates deep underwater valleys known as oceanic trenches, which are areas where one plate slides beneath another in a process called subduction.

These trenches do not only shape the country’s underwater landscape but also explain why earthquakes in the Philippines are common and sometimes powerful. By understanding where these trenches are located, scientists can better monitor potential seismic activity and help communities prepare for future events.

1. Philippine (Mindanao) Trench – The Deepest and Most Active Trench

Located east of Mindanao and Samar, the Philippine Trench, also known as the Mindanao Trench, is among the deepest parts of the world’s oceans, reaching about 10,540 meters. It marks the boundary where the Philippine Sea Plate is subducting beneath the Eurasian Plate, making it a key source of deep and powerful earthquakes.

2. East Luzon Trench – A Major Source of Seismic Activity in Northern Luzon

Found east of northern Luzon, this trench marks the subduction of the Philippine Sea Plate beneath the Luzon region. It is responsible for frequent undersea earthquakes that occasionally generate tsunamis affecting eastern Luzon.

3. Negros Trench – A Key Subduction Zone in the Visayas Region

Situated west of Negros Island, the Negros Trench represents the subduction of the Sunda Plate beneath the Philippine Mobile Belt. Movements along this trench can trigger moderate to strong earthquakes that affect the Visayas region.

4. Sulu Trench – A Lesser-Known but Significant Tectonic Feature

Positioned southwest of the archipelago near the Sulu Sea, the Sulu Trench results from the interaction of the Sulu microplate with the Sulu Sea basin. Although less active than other trenches, it contributes to the complex tectonic structure of southern Philippines.

5. Cotabato Trench – An Active Earthquake Zone in Southern Mindanao

Running parallel to southern Mindanao, this smaller trench is formed by the subduction of the Celebes Sea Plate beneath the island. It has produced several significant earthquakes in the Cotabato and General Santos areas.

Bonus: Manila Trench – A Western Boundary Linked to Strong Earthquakes and Tsunamis

Stretching along the western side of Luzon toward Taiwan, the Manila Trench is sometimes included as a sixth major trench influencing the Philippines. Although it lies slightly outside the Philippine Sea Plate system, it is closely monitored because of its potential to generate strong earthquakes and tsunamis that could impact western Luzon and Metro Manila.

In summary, whether you count five or six, these oceanic trenches reveal the powerful forces beneath the sea that continuously shape our islands. Each trench reminds us that the frequent earthquakes in the Philippines are part of an ever-evolving geological process that defines our country’s natural landscape.