EXPLAINER: Why is PHIVOLCS studying Cotabato Trench after Mindanao earthquake?

A strong earthquake surprised residents in a large portion of Mindanao on the morning of June 8, 2026. The air was filled with screams and cries of students on the first day of classes!

One of the possible causes being looked at is the Cotabato Trench. But why is PHIVOLCS examining the Cotabato Trench? Watch the video.

The residents of General Santos City could only scream in fear as a building collapsed right before their eyes after a 7.8 magnitude earthquake in the region.

Terror greeted students and teachers of the Mahayahay Elementary School on the first day of classes for the School Year 2026 - 2027.

The screams and cries of children can be heard as they sat helplessly on the ground while it continued to shake.

In just a few moments, a shelter suddenly toppled causing students and teachers to run for safety.

School officials said no one was hurt from the incident.

The flag ceremony at the Malalag, Davao del Sur School of Fisheries had to stop due to the strong tremors.

A covered court was filled with terrified screams as teachers and students fled while the ground shook uncontrollably.

Pandemonium ensued inside the GenSan Airport as a result of the strong earthquake.

A video uploader shared how they felt consecutive aftershocks outside the airport.

A tsunami warning was raised in a large part of Mindanao after the region was hit by a 7.8 magnitude earthquake on June 8, 2026.

In an advisory of the Philippine Institute of Volcanology and Seismology (PHIVOLCS), the earthquake occurred at around 7:37 a.m. and was initially reported to be magnitude 7 and a depth of 10 kilometers.

But in its second advisory, PHIVOLCS upgraded the strength of the quake to magnitude 7.8 and the depth was corrected at 33 kilometers.

The epicenter was placed at the following coordinates: 05.57°N, 124.98°E, or 32 kilometers southwest of the town of Maasim, Sarangani.

As of 11 a.m., 138 aftershocks were recorded by PHIVOLCS. Among these aftershocks, nine were felt by residents, and strengths ranging from magnitude 1.3 to 6.7.

The death toll caused by the strong earthquake has risen to eight , according to the Office of Civil Defense (OCD), as of 1 p.m., which is based on reports from the Local Disaster Risk Reduction and Management Councils.

The Philippine National Police listed 20 structures as damaged in the Soccsksargen region. Among the 14 affected facilities are commercial establishments, two schools, two hospitals, and two residential houses.

PHIVOLCS is now studying whether the strong tremor in Mindanao has connection with the Cotabato Trench.

According to PHIVOLCS Director Teresito Bacolcol, the data is currently being examined to determine the exact cause of the strong earthquake.

“So far nasa Sarangani Bay ito. Tinitingnan natin if this is related to the Cotabato Trench,” he said.

The Cotabato Trench is a deep underwater trench located southwest of Mindanao, and is near the provinces of Sultan Kudarat, Maguindanao, and South Cotabato.

It was formed by the subduction of the oceanic crust underneath the Philippine Mobile Belt, where the tectonic plates meet and stress accumulates, eventually resulting in the form of earthquakes.

According to PHIVOLCS, the Cotabato Trench remains a highly active seismic feature and has the capacity to cause moderate to strong tremors, including megathrust earthquakes.

Historical records and seismic studies connect the Cotabato Trench with disastrous earthquakes such as the 1976 Moro Gulf earthquake and tsunami.

On August 17, 1976, a magnitude 8.1 tremor struck near the Moro Gulf along the Cotabato Trench and resulted in a tsunami that killed an estimated 8.000 people in Mindanao.

In Tsunami Information No. 2 that was was released at 3:19 p.m., PHIVOLCS cancelled the tsunami warning after it was observed that the tsunami wave was too small to cause damage.

Despite the cancellation of the warning, PHIVOLCS urged coastal communities to remain observant, especially in the event of strong aftershocks.

The agency also reminded the public to remain alert for natural signs of tsunami such as strong earthquakes, the sudden rise or fall of sea levels and the sound of approaching waves. —RF, GMA News