The Philippine Institute of Volcanology and Seismology (Phivolcs) in Cebu has warned that the province remains vulnerable to a major earthquake due to the presence of active fault systems across the island.

However, engineer Robinson Jorgio, director of the Phivolcs Visayas Cluster Monitoring Center for Earthquake and Tsunami, clarified that no earthquake swarms have been recorded in Cebu in recent months.

An earthquake swarm refers to a series of small to moderate earthquakes occurring within the same area over a relatively short period, ranging from days to months. According to Jorgio, while earthquake swarms can sometimes precede a stronger quake, they do not automatically indicate that a destructive earthquake will follow.

He cited the Bogo Bay Fault as an example, where a series of earthquakes was recorded beginning in April before a stronger earthquake struck on 30 September.

Despite the absence of recent earthquake swarms, Phivolcs said Cebu remains susceptible to a major seismic event because of its active fault systems.

“Every fault has its own ‘Big One.’ Since we have a potentially active fault in Cebu, we also have a possible ‘Big One.’ Our estimate is that it could reach a magnitude of 7.2 to 7.5,” Jorgio said.

The Central Cebu Fault System has been identified as a network of potentially active faults that passes through densely populated areas, including Cebu City, Mandaue City, Talisay City and Danao City.

Jorgio said an earthquake of magnitude 7.2 to 7.5 could generate Intensity VIII shaking.

Under the Phivolcs Earthquake Intensity Scale, Intensity VIII is classified as “very destructive” and can cause serious damage to buildings, roads, bridges and other infrastructure.

Earthquakes occur as tectonic plates beneath the Earth continuously move and exert pressure on fault lines and ocean trenches surrounding the Philippines. As stress accumulates over time, faults may eventually rupture and release energy in the form of an earthquake.

Cebu was not significantly affected by the recent magnitude 7.8 earthquake that struck off Sarangani and nearby areas in Mindanao.

In response to the threat of a possible major earthquake, Cebu Governor Pamela Baricuatro said the provincial government is intensifying its disaster preparedness efforts.

“I woke up thinking about it first thing in the morning. I was already in conversation with Colonel Pastor (Provincial Disaster Risk Reduction and Management Office head) about what we should do,” Baricuatro said.

The governor noted that preparedness has become a priority following the earthquake that struck northern Cebu last year.