Movement of Cotabato Trench caused earthquake

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June 9, 2026 | 12:00am

MANILA, Philippines — Monday’s powerful magnitude 7.8 earthquake off Maasim, Sarangani was likely caused by subduction activity along the Cotabato Trench, according to Science Secretary Renato Solidum Jr.

The Cotabato Trench, located off the southwestern coast of Mindanao, is part of a complex system of subduction zones where tectonic plates interact. It has been linked to several major earthquakes that struck Mindanao over the past century, including the magnitude 8.3 earthquake in 1918, the magnitude 7.9 earthquake and tsunami in 1976, and the magnitude 7.5 earthquake in 2002.

Solidum said the latest quake mirrors previous seismic activity in the area.

“There were two recent strong earthquakes in the area offshore of Sarangani also related to the subduction along the Cotabato Trench: magnitude 7.2 on April 29, 2017, and magnitude 6.8 on Nov. 17, 2023,” the science chief said.

Data showed the April 2017 earthquake injured five people and damaged homes and schools, while the November 2023 quake left 11 people dead, 37 injured and more than 6,000 homes damaged.

Solidum noted that all three events were shallow earthquakes, occurring at depths of 53 kilometers in 2017, 63 kilometers in 2023 and 33 kilometers in Monday’s quake.

“If the earthquake depth is shallower and on land, then the intensity can be higher compared to an earthquake that is deeper and offshore,” Solidum explained.

“Earthquakes with a depth of 33 kilometers are considered shallow, but intensities are determined by the depth and the distance of the epicenter to the locality,” he added.

The strongest shaking was recorded at Intensity VIII in Malapatan, Sarangani, while Intensity VII was felt in General Santos City, Koronadal City and Santa Maria, Davao Occidental.

Solidum also clarified that the Sarangani earthquake was unrelated to the twin earthquakes that struck Davao Oriental in October 2025.

Structural damage

As authorities continued to assess the extent of the damage, Public Works Secretary Vince Dizon arrived in General Santos City yesterday with officials from the Office of Civil Defense, Department of Education, Department of Social Welfare and Development, and Department of Health to inspect damaged infrastructure and coordinate response efforts.

Upon arrival, Dizon said the immediate priority was to determine the extent of the damage and ensure access for relief operations.

“We need to conduct an assessment first, and then let’s make sure all national roads are passable for relief operations,” Dizon said.

The Philippine Ports Authority, meanwhile, reported only minor structural damage at the Port of General Santos.

Meanwhile, the Philippine Insurers and Reinsurers Association Inc. said it is too early to determine insured losses, noting that claims are only beginning to be reported and a complete assessment could take several weeks. — Aubrey Rose Inosante, Evelyn Macairan, Rainier Allan Ronda