June 2, 2023

Expect more landslides and rockslides to occur at the mountainous areas of the Cordillera due to the presence of tension cracks and liquefaction in slopes as a result of the magnitude 7.0 earthquake that hit most of northern Luzon on July 27, the Philippine Institute of Volcanology and Seismology (Phivolcs) warned.

Aftershocks and the expected rains and typhoons could trigger rocks and soil to erode from already precarious mountains in the region said Phivolcs Associate Scientist Arturo Daag in a briefing on the disaster response of various agencies in Abra – the province badly hit by the earthquake.

Daag said a team from the Phivolcs central office has been deployed in Benguet, Baguio, Mountain Province, and Abra to monitor liquefaction-prone areas and mountainous areas that have tension cracks.

Findings of the team will be referred to concerned offices for implementation of short, medium, and long-term interventions.

Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake. It occurs when vibrations from seismic waves increase water pressure between soil grains, transforming once cohesive soil into mud.

Tension cracks in slopes on the other hand, act as pathways for rainfall to infiltrate into soil and leads to rapid permeability and decrease in strength of soil resulting in landslides.

As of Aug. 2, the Phivolcs has recorded over 2,000 aftershocks with average magnitude of between intensity 1.5 and 5.4.

The earthquake itself and aftershocks can also trigger buildings and other structures to weaken and possibly collapse.

Office of Civil Defense-Cordillera director and Regional Disaster and Risk Reduction Management Council chair Albert Mogol said the recent earthquake should serve as a reminder to the community and other stakeholders to be proactive to avoid or minimize displacement of communities, damage to property, vital infrastructure, and loss of lives, and injury.

As part of preventive measures, he suggested that local government units must periodically inspect buildings to ensure that these remain structurally sound.

He reminded that with Baguio’s proximity to the Tubao Fault, an earthquake more destructive than the July 16, 1990 and July 27 earthquakes are possible.

“These are possible scenarios so our buildings should be able to withstand an intensity 8 earthquake,” Mogol said.

Future programs should also include for LGUs to identify open spaces where emergency shelters could be set up quickly and then kept in warehouses after a calamity, Mogol said.

He said the Phi-lippines can follow the model being implemented by the Federal Emergency Management Agency which has prefabricated shelters ready to be set up during a calamity then disassembled after evacuees return to their homes.

In the Simulated Intensity of Ground Shaking in the Cordillera prepared by the Phivolcs in 2002, La Union, Benguet (including Baguio), eastern Pangasinan, Ifugao, and Nueva Vizcaya are expected to experience an intensity 8 or a destructive earthquake if the Tubao Fault moves.

Other provinces in the region like Apayao, Kalinga, and Abra, which are all near the Cagayan Valley Fault, are also likely to experience intensity 8 earthquake, according to the Phivolcs.  The magnitude 7.0 earthquake has so far affected 284,898 individuals; 76,836 families; and 543 barangays in the Cordillera. – Rimaliza A. Opiña