U.P. Diliman is situated near West Valley Fault Line - Government geologists

West Valley Fault Line near U.P. Diliman
Source: Phiilvolcs

MANILA, Philippines - Government geologists have found evidence of ground displacement along the West Valley Fault line, validating earlier warnings by national and local authorities that the fault - running 7.2 kilometers from Parañaque through Makati, Taguig, Marikina, to San Mateo along the periphery of Quezon City - remains active.

This came to light as the Quezon City government and the Philippine Institute of Volcanology and Seismology (Phivolcs) on Monday completed trenching work across the West Valley Fault line at Barangay Bagong Silangan, Novaliches. Intended to identify ground rupture movements and slip rates across the fault, the trenching activities found abrupt changes in sediment layers in the area, Quezon City officials said.

The activity involved excavations of two trenches, about 50 meters apart, within a 50-hectare property owned by Banco Filipino at Barangay Bagong Silangan. The area, according to a Metro Manila Earthquake Impact Reduction Study (MMEIRS), shows high susceptibility to earthquakes, along with Barangay Payatas, also in Novaliches.

The exposed trench walls indicated that at least two to three earthquake events had in fact already taken place in the area in the past. Phivolcs is now collecting charcoal pieces for carbon-14 analysis to determine the approximate time of the occurrence of the said earthquakes and the estimate of the age of the sediment layers affected by the ground displacement.

"The Phivolcs findings just validated the claim that the West Valley Fault Line is indeed active," said Elmo San Diego, action officer of the QC disaster risk reduction management council and head of the city's department of public order and safety. The MMEIRS suggests that a magnitude 7.2 earthquake may originate at the West Valley Fault line at some point in the future.

San Diego reiterated QC Mayor Herbert Bautista's call to declare the 7-kilometer stretch of the fault system that runs through QC's periphery a danger zone. "The safety of our residents, particularly those living on top of the fault line, is non-negotiable," San Diego said. "The fault line is unlivable."

The fault line cuts across major cities in Metro Manila, and has in its path scores of large subdivisions and schools. Ateneo de Manila and the University of the Philippines in Diliman are both situated near or atop the fault line which has not moved in 200 years, but which Phivolcs had warned may therefore be "ripe for movement".

Batasan Hills in the northern stretch of the fault has within its vicinity the House of Representatives of the Philippines. To the south, subdivisions such as Green Meadows, Valle Verde, and McKinley Hills all sit atop the fault. Ayala Heights in Quezon is similarly situated in an area within the potential influence of movements along the line.

(Philippine News Agency)