Fatalities from the magnitude 7.8 Mindanao earthquake reached 37, with four deaths in Region 11 and 33 in Region 12, prompting authorities to place General Santos City under a state of calamity.
Phivolcs Director Robinson Jorgio clarified that the earthquake was generated by the Cotabato Trench and has no direct link to active fault systems in Cebu or the rest of Central Visayas.
Phivolcs plans to deploy additional seismographs and monitoring equipment in Cebu and Bohol by the end of 2026 to strengthen regional fault monitoring despite current instrument limitations.
FATALITIES from the magnitude 7.8 earthquake that struck Mindanao climbed to 37 on Tuesday, June 9, 2026, as the Philippine Institute of Volcanology and Seismology (Phivolcs) 7 said the quake was generated by the Cotabato Trench and had no direct link to active fault systems in Cebu and the rest of Central Visayas.
The National Disaster Risk Reduction and Management Council (NDRRMC) said that as of 6 a.m. Tuesday, four deaths were recorded in Region 11 (Davao Region), while 33 were reported in Region 12 (Soccsksargen).
Office of Civil Defense (OCD) deputy spokesperson Diego Mariano said the Region 12 fatalities were recorded in Sarangani with 18, General Santos City with 12 and South Cotabato with three.
General Santos City was placed under a state of calamity following the quake, which damaged structures, vital installations, bridges and roads.
Energy Secretary Sharon Garin said electricity in quake-affected areas had been almost fully restored.
The earthquake occurred at 7:37 a.m. Monday, June 8, and was located about 32 kilometers south-southwest of Maasim, Sarangani, at a depth of 33 kilometers. The tremor was felt across large parts of Mindanao, prompting authorities to assess damage in affected areas.
Separate fault systems
During a media forum in Cebu City, Department of Science and Technology-Phivolcs Visayas Cluster Monitoring Center Director Robinson Jorgio said the Cotabato Trench, located off Mindanao, is separate from the fault systems being monitored in the Visayas.
“This is generated by the Cotabato Trench. A few years ago there was a magnitude 6.8 within that area. Early this year we recorded swarms related to the Cotabato Trench,” Jorgio said.
“Early this year we recorded continuous earthquakes of lesser magnitude within that area. So, those were foreshocks related to this magnitude 7.8 because they were generated by the same source, the Cotabato Trench,” he added.
Jorgio said earthquake swarms refer to a series of smaller earthquakes occurring in the same area over a period of time, while earthquakes that occur after a major quake are classified as aftershocks.
He said the country’s trenches and fault systems are products of tectonic plate movements that continue to compress the Philippine archipelago.
“Our trenches and fault systems are products of major plate tectonics which are pushing or squeezing the Philippine archipelago. The weakest portion of the system will rupture first and create an earthquake,” Jorgio said.
However, Jorgio said the Cotabato Trench is far from the fault systems in Central Visayas.
“We have to understand that the Cotabato Trench is far from our fault systems in the Visayas, particularly in Cebu,” Jorgio said in Cebuano.
“The Big One”
The Mindanao quake renewed public discussion on the “Big One,” a term commonly used to refer to a possible major earthquake that could affect heavily populated areas. It refers to a predicted magnitude 7.2 earthquake along the 100-kilometer West Valley Fault, which is expected to cause widespread destruction in Metro Manila.
In Cebu, Jorgio said potentially active faults could also generate a major earthquake, adding that a strong quake in Cebu could reach magnitude 7.2 to 7.5 and produce Intensity 8 ground shaking across the island.
However, Phivolcs said the timing of such a major earthquake remains uncertain, and the agency continues to monitor ground movements.
Monitoring in Cebu
Phivolcs continues to monitor active faults in the region. Jorgio said a temporary seismic system remains operational in northern Cebu, particularly in Bogo City, where a magnitude 6.9 earthquake struck on Sept. 30, 2025.
“In Bogo, our monitoring remains continuous. We still have augmented temporary seismic stations there so we can obtain complete data,” he said in Cebuano.
Jorgio said monitoring all active faults at the same time remains difficult because of the limited number of instruments available.
“Here in Cebu, we monitor all faults within the Visayas, but we cannot monitor all of them at the same time because the number of instruments we can deploy is limited,” he said.
To strengthen earthquake monitoring, Phivolcs plans to install additional instruments in Cebu and Bohol before the year ends.
The planned expansion includes additional seismographs, accelerometers and GPS-based ground deformation monitoring equipment.
Preparedness urged
Jorgio reminded the public that earthquake preparedness remains crucial regardless of where a major earthquake occurs.
He advised residents to know the structural condition of the buildings they occupy and determine whether these can withstand strong ground shaking.
“If we know that our building is structurally sound, our first reaction should be to protect ourselves from falling debris. We should duck, cover and hold,” Jorgio said in Cebuano.
He also urged local governments to continue hazard assessments and planning. Phivolcs, he said, has been working with local officials in Cebu and Mandaue City to improve disaster preparedness through exposure and vulnerability mapping.
Phivolcs said continuous monitoring and public preparedness remain essential as active faults and trenches across the country continue to generate earthquakes. / TPM, APRIL VINCE VILLACORTA AND JUSTIN JOHN BUGTAI, CNU INTERNS