Dormant Underwater Fault, Root of Severe Cebu Earthquake

A 400-year-dormant offshore fault caused the tragic quake in Cebu and nearby provinces on 30 September 2025, according to the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

“At least in the last 400 years, yun pong fault na nag-generate dito, ngayon lang po uli s’ya gumalaw,” said Dr. Winchelle Ian G. Sevilla, chief of the Seismological Observation and Earthquake Prediction Division of the PHIVOLCS in a press briefing on 01 October 2025.

[Only now that the fault that caused this [earthquake] made a movement after the last 400 years.]

Sevilla explained that historically, there were few tremors that took place in the vicinity of the epicenter, Bogo City, especially in the northern area. These past shakes, however, reached not greater than magnitude five, which were essentially not perceptible to the residents.

The long inactivity of the fault amplified its destructive strength.

“So medyo matagal po s’yang [hindi] gumalaw kaya s’ya medyo malakas,” Sevilla noted.

[The fault did not make any movement for a long period. That’s why it was quite strong.]

The PHIVOLCS presently cannot identify what fault caused the quake as this land crack does not exist in the bureau’s Distribution of Active Faults and Trenches in the Philippines chart. Said absence, Sevilla noted, is mainly due to the fault’s underwater location. Further, only minor earthquakes have been recorded in the epicentral area, posing no major threats for the PHIVOLCS to draft a fault map of the area.

Sevilla also informed that the fault took place near towards the seabed, estimated at five kilometers towards the surface, making it stronger and more perceptible, compared with a fault that occurred well beneath the surface.

Yesterday, 30 September, at 9:59 P.M., a magnitude 6.9 earthquake jolted the entire Cebu and nearby localities.

Various structures crumbled, including commercial buildings and heritage churches.

The government has thrown its massive support to the search, rescue, and relief operations for the residents of Cebu, tapping the Philippine National Police, Philippine Coast Guard, and Armed Forces of the Philippines to reinforce the efforts.

Department of National Defense secretary Gilberto Teodoro Jr. flew to Cebu to assess personally the situation in the earthquake-torn area.

Various government agencies, among which are the Department of Public Works and Highways, Department of Health, Department of Social Welfare and Development, and Department of Energy, are also bent to alleviate the adverse condition of the province.

The Department of Budget and Management, for its part, has called upon concerned government agencies to roll their quick response funds (Q.R.F.s), a financial resource that enables these offices to respond to disasters such as earthquakes and typhoons.