October 9, 2025
CEBU CITY – A week after the powerful magnitude 6.9 earthquake rocked northern Cebu, thousands of aftershocks continue to jolt affected communities, keeping many families too afraid to return home.
As of 8 a.m. on Wednesday, October 8, the Philippine Institute of Volcanology and Seismology (Phivolcs) has recorded 9,188 aftershocks, ranging between magnitude 1 and 5.1 on the Richter scale, since the September 30 main shock.
Of these numbers, 38 have been felt.
READ: Cebu earthquake: 5-meter buffer zone in Bogo Fault set by Phivolcs
These repeated tremors explain why most of the 412,000 affected individuals remain in temporary shelters or evacuation areas.
Phivolcs said the number of daily aftershocks has started to decline, but it urged residents to stay alert and avoid danger zones, especially those near sinkholes and the recently identified Bogo Bay Fault.
“Bagamat bumababa na ang bilang ng aftershocks, may posibilidad pa rin na magkaroon ng malalakas na aftershock sa mga susunod na araw (While the number of aftershocks has decreased, there is still the possibility that a strong aftershock may occur in the coming days),” the agency said, warning that strong tremors may still occur not only along the Bogo Bay Fault but also in other active faults in and around Cebu Island.
Why aftershocks happen
Aftershocks are smaller quakes that occur after a major earthquake. They can last between weeks and even up to months.
According to the United States Geological Survey (USGS), they usually happen close to the main fault line and become less frequent over time as the Earth’s crust gradually settles.
The source of the September 30 quake in northern Cebu was the recently identified Bogo Bay Fault Line.
The temblor was shallow, occurring only five kilometers below ground, which explains why it has produced an unusually high number of aftershocks, around 10,000, with 38 felt by residents.
In comparison, deeper earthquakes, those occurring more than 30 kilometers underground, rarely generate this many or this strong aftershocks.
‘Normal part of adjustment’
Dr. Teresito Bacolcol, Phivolcs director, said aftershocks are a natural part of the Earth’s adjustment process following a strong quake.
He compared them to a ruler that vibrates after being bent and released.
Up to 2,000 aftershocks may occur within the first 24 hours after a major tremor, but both their frequency and intensity quickly decrease over time, he explained.
“By the 10th day, the number of aftershocks will likely drop to around 200 to 300, and by the 100th day, only 20 to 40 minor tremors are expected—most of which are too weak to be felt,” Bacolcol said.
He added that while some minor aftershocks may still occur until December, these are expected to be much weaker and not dangerous.
‘No build zones’
In the meantime, as relief and recovery efforts continue in the affected areas, Phivolcs assured the public that they may rebuild their homes and other structures as long as these do not fall under identified danger zones.
The bureau has earlier recommended a five-meter buffer zone on both sides of the Bogo Bay Fault that traverses from the sea and across Bogo City inland.
Likewise, the Office of Civil Defense (OCD) urged residents in landslide-prone and other geologically unstable areas to relocate to safer places.
The 6.9 earthquake last September 30 was the deadliest in Cebu province in recent history, killing at least 70 and injuring over 1,000 more.