THE discovery of the Bogo Bay Fault Line has far-reaching implications for Cebu, as it paves the way for more accurate active fault mapping to help local governments identify high-risk areas, according to the Philippine Institute of Volcanology and Seismology (Phivolcs).
Phivolcs Director Teresito Bacolcol told SunStar Cebu in a phone interview on Sunday, Oct. 5, 2025, that the fault’s discovery enables local government units (LGUs) to avoid building infrastructure in high-risk areas.
He explained this is crucial for LGU planning, as it allows engineers to consider the fault line’s presence when designing high-rise buildings and residential structures. He added it improves their Comprehensive Land Use Plans by accurately identifying fault-affected areas.
“You’re not supposed to build any structure directly on top of an active fault,” said Bacolcol. “This is very important for their planning because our recommendation is a five-meter buffer zone on both sides of the fault.”
The fault, discovered on Friday, Oct. 3, also allows Phivolcs to update both the active fault map and tsunami assessments, particularly since the fault is located offshore.
The Bogo Bay Fault Line has been confirmed as the source of the magnitude 6.9 offshore earthquake in northern Cebu on Tuesday, Sept. 30. This was the first reported major earthquake in Cebu over the last 400 years.
Potential active faults
Bacolcol explained that there are three types of fault lines, with the Bogo Bay Fault identified as a strike-slip fault, where blocks slide past each other horizontally.
The other two types are normal faults, where blocks move apart due to tension, and reverse faults, where blocks are pushed together by compression, causing the hanging wall to move upward.
Bacolcol noted that there are “potentially active” fault lines in the central part of Cebu.
He urged everyone to remain vigilant, practice the “drop, cover and hold,” and stay away from infrastructure weakened by the quake. / DPC