THE Mines and Geosciences Bureau in Central Visayas (MGB 7) has issued a subsidence threat advisory after sinkholes and land subsidence were confirmed in several municipalities in northern Cebu following the magnitude 6.9 earthquake that struck the province on September 30, 2025.
MGB 7, in an advisory released on Friday, October 3, warned the mayor of Medellin, Cebu, that all barangays with reported sinkhole occurrences have been classified under a high subsidence hazard rating.
The bureau said the sinkholes, particularly those caused by cover collapse, pose serious threats to life, property, and infrastructure.
Land subsidence, according to MGB, is the lowering of the land surface which occurs rapidly due to a sinkhole collapse or during a major earthquake.
MGB 7 said ground cracks and depressions were also observed in affected areas, suggesting that the subsidence could worsen over time.
MGB7 recommended the following:
• Restrict and install warning signs. Restrict access to sinkhole-affected and crack-prone areas until further assessment by installing caution tapes, cordons, and warning signages to inform locals and road users of the subsidence threat. Report any similar occurrences to the Mines and Geosciences Bureau Region 7;
• Refrain from covering or backfilling the sinkhole unless recommended by authorities, especially if a subterranean river or creek is identified beneath it. Covering the sinkhole may result in water ponding and could induce further subsidence in the immediate vicinity;
• Monitor any further movement of the tension cracks around the sinkhole, particularly after periods of heavy rainfall;
• Discourage further development or community growth in the area, as the sinkhole may be connected to a larger cave or subterranean river system. Additional loading from structures or activities may trigger further collapse;
• Conduct a specific geotechnical study to determine the extent of the cave system (if present) and identify appropriate engineering measures to mitigate the hazard.
MGB 7 also advised the local chief executive of Medellin to initiate readiness measures for this identified geohazard, considering sinkhole development may progress due to rainfall, changes in the water table, or further seismic activity.
Two teams of geologists from MGB 7 and the MGB Central Office have been deployed to inspect both landslide-hit zones and sinkhole sites.
The bureau said its findings and further recommendations will be relayed to concerned local governments and communities.
Aside from Medellin, MGB 7 also issued advisories to the mayors of San Remigio, Tabogon, Daanbantayan, and Bogo City. (JJL)