THE swarm of earthquakes that has shaken offshore areas of Sultan Kudarat over the past several days is linked to tectonic movements along the Cotabato Trench, a major undersea fault system capable of generating strong earthquakes, according to the Philippine Institute of Volcanology and Seismology (Phivolcs).
Phivolcs Executive Director Dr. Teresito Bacolcol said the cluster of tremors was probably caused by the gradual release of stress along the trench.
“The generator of these events is the Cotabato Trench,” he said in a message to a national news report.
Bacolcol noted that while the earthquakes are tectonic in origin, there are currently no clear signs that the swarm is a precursor to a larger earthquake, although such a possibility cannot be ruled out.
Hundreds of tremors recorded
In an advisory issued Thursday, January 22, 2026, Phivolcs reported that 633 offshore earthquakes had been recorded in Sultan Kudarat as of 12 noon. Of these, 197 earthquakes were plotted, while 30 were felt by residents.
The earthquake swarm began on January 19, with magnitudes ranging from 1.4 to 5.2. The strongest event, a magnitude 5.2 tectonic earthquake, struck at 9:33 a.m. at a depth of 10 kilometers.
Phivolcs located the epicenter at 06.39°N, 123.72°E, around 40 kilometers south-southwest of Kalamansig, Sultan Kudarat. Instrumental intensity IV was recorded in Lebak, Sultan Kudarat.
Following the stronger shaking, classes across the province and government work in three municipalities were suspended as a precaution.
In a subsequent update, Phivolcs said the number of recorded aftershocks had climbed to around 765 as of 6 a.m. Friday, January 23, with magnitudes still ranging between 1.4 and 5.2.
The Cotabato Trench and why it matters
The Cotabato Trench is a deep undersea trench located off the southwestern coast of Mindanao, stretching near Sultan Kudarat, Maguindanao, and South Cotabato. It is formed by the subduction of oceanic crust beneath the Philippine Mobile Belt, where tectonic plates converge and store stress that is eventually released as earthquakes.
According to Phivolcs and international geophysical studies, the trench has been active for millions of years and is capable of producing moderate to large earthquakes, including megathrust events. Historical records and seismic research link the trench to destructive earthquakes such as the 1918 Celebes Sea earthquake and the 1976 Moro Gulf earthquake, which triggered a deadly tsunami.
Scientists explain that earthquake swarms, like the one currently being observed, occur when stress is released gradually along sections of an active trench or fault, rather than through a single major rupture. These swarms can involve hundreds of small to moderate earthquakes over days or weeks and do not necessarily culminate in a stronger event.
However, Phivolcs emphasized that the Cotabato Trench remains a significant seismic and tsunami source, underscoring the importance of continuous monitoring, public preparedness, and adherence to safety advisories in coastal and nearby inland communities.
Phivolcs said it will continue to closely monitor seismic activity in the area and urged the public to stay informed through official bulletins. DEF