Fault Markers Indicate Where Quake May Hit

National agencies and the city government of Davao initiated Sunday (June 23) the “Walk the Fault” activity marking the sites traversed by earthquake faults Lacson and Dacudao located in the city’s third district.

Together with the City Disaster Risk Reduction and Management Office, Office of Civil Defense XI, and line agencies of government under the Regional Disaster Risk Reduction and Management Council and officials of Barangays Bago Oshiro and Mintal, the Philippine Institute of Volcanology and Seismology (Phivolcs) inspected the site and put markers corresponding to the path.

First to be visited was Purok 7 at Barangay Bago Oshiro where the Lacson Fault is located. The areas affected are basically farmlands.

In contrast to Barangay Bago Oshiro are the sites in Barangay Mintal.

The Dacudao Fault traverses the areas in Barangay Mintal that are basically residential and largely populated.

Phivolcs said the Dacudado Fault passes from Ulas to Calinan via Barangay Mintal and even cuts into half the local seat of governance like the barangay hall and Police Station Number 9 or the Mintal Police Station.

Kathleen Papiona, senior science research specialist of the Philippine Institute of Volcanology and Seismology, clarified that these faults have not moved for several hundred years.

She stressed that despite this status, the residents must be aware of the possible faults that might move right in their vicinity.

Papiona said Lacson and Dacudao Faults are classified as reversed faults, where the cracks are hidden or under the ground.

“We call these faults the Central Davao Fault System, which has five segments identified as Tamugan Fault, Lacson Fault, Dacudado Fault, Pangyan-Biao Escuela Fault and the New Carmen Fault. Lacson Fault traverses Bago Oshiro which moves in a thrust manner where one part or one block of the other side of the fault moves up. Usually the fault does not show on the surface,” she said.

Papiona said the other side of the fault usually swells while the other remains lower.

She said ground-shaking is stronger on the side that swells compared to the lower ground.

Papiona also said a reversed fault has a wider deformation zone where the crack on the ground could manifest.

She said that the one with the marker is the best estimate of where the fault is.

Undersecretary Renato Solidum, director of Phivolcs, explained that if the fault is well defined, building can be done five meters away from the fault which serves as the buffer zone.

He said counting of five meters can be done only at the tip of the fault especially on faults that have deformation.

“It means no build zone is wider because of wider deformation zone compared to a linear fault. It is important that we learn to differentiate the well-defined fault or the fault with wider deformation,” Solidum said.

Alfredo Baluran, chief of the City Disaster Risk Reduction and Management Office, suggested that faults must be identified permanently.

He suggested that every barangay government must put up a permanent marker either on the boundary of private property or any public land which the fault traverses so that the economic activity of the land owner will not be affected.

Baluran said barangay functionaries must lead the awareness campaign by putting a marker on these faults and warn the public of the relevance of the information that the marker indicates where the fault is. (PIA XI)