On the afternoon of July 16, 1990, college student Eddie Tanguilig was enjoying his first ever game of billiards during a month-long students’ strike over tuition fee hikes when he felt the ground shaking. People began to scream and run out of the buildings. From a building called Castilla Monte near Burnham Park, Tanguilig instinctively ran along with the crowd, all the while thinking of his siblings who were left at home in Tuba, west of Baguio City. “Sobrang gulo, lahat nagpa-panic, nag-iiyakan. Halu-halo ang mga tao at sasakyan sa daan. Akala mo katapusan na ng mundo," recalls Tanguilig, who was then 18 years old. Amid the chaos, Tanguilig clearly remembers seeing structures along Harrison Road collapse right before his eyes. One of these buildings was the Baguio Park Hotel, which was reduced to rubble in an instant. Two decades hence, last January 12, a magnitude-7.0 tremor hit the Caribbean nation of Haiti, the poorest country in the Western Hemisphere. Its capital, Port-au-Prince, crumbled much like Baguio City and suffered more massive losses and deaths. “Mas malala iyong nangyari sa Haiti," Tanguilig observes. Upon seeing the devastation on television, he felt lucky to have survived the stronger magnitude-7.8 tremor that shook his hometown two decades ago. Five-meter buffer zone Some 300 kilometers away, Metro Manila did not suffer as much as Baguio City in 1990, but experts say its residents cannot afford to be complacent. The active Valley Fault System, more widely known as the West Valley Fault, that traverses the nation’s capital can move anytime.
Monitoring the West Valley Fault The Valley Fault System, formerly called and still widely known as the West Valley Fault System, is one of the country’s most active faults. It stretches from the Sierra Madre in Bulacan and goes on down to Tagaytay, traversing parts of Metro Manila and Laguna. PJ Delos Reyes, Officer-in-Charge of Phivolcs' Geology Department, says an active fault is characterized by recorded movements in the last 10,000 years. Earthquakes frequently originate from these places, and certain landforms such as a "continuous linear offset of river systems" that are evident in the West Valley Fault, for instance, are observed. A study done in 2000 by the United States Geological Service and Phivolcs found out that the West Valley Fault has moved two to four times over the past 1,300 to 1,700 years, according to Dr. Alfredo Mahar Lagmay of the National Institute of Geological Sciences (NIGS). The study concluded that "a range of 200 to 400 years… should be used in assessing the potential future recurrence of large earthquakes on the West Valley fault system." The West Valley Fault’s last known activity was 200 years ago, which means an earthquake could occur anytime, says Lagmay. Phivolcs has installed Global Positioning System (GPS) devices along some parts of the fault to continuously record its seismic activities. So far, no significant movement from the West Valley Fault has been detected, according to Delos Reyes. The Metro Manila Impact Reduction Study conducted in 2004 by the Philippine Institute of Volcanology and Seismology (Phivolcs), the Metro Manila Development Authority (MMDA), and the Japan International Cooperation Agency (JICA) found that the capital is vulnerable to a magnitude-7.2 earthquake that may be generated by the West Valley Fault. The study assessed Metro Manila’s preparedness and estimated that there could be 35,000 fatalities, 500 simultaneous fires in up to 98,000 buildings, and 170,000 structures may collapse in the event of strong temblors. “If a structure is directly on top of an active fault line, then that structure will be completely destroyed," says Dr. Alfredo Mahar Lagmay of the National Institute of Geological Sciences (NIGS) at the University of the Philippines. Adam Abinales, president of the Association of Structural Engineers of the Philippines, agrees: “The damage to be incurred by a building which happens to be standing directly on top of a fault line will be greater than that from a building farther away from it." In metropolitan Manila, which has a population of around 10 million, the active fault traverses parts of Quezon City, Pasig, Taguig, and Pasay. Housing subdivisions, commercial centers, and several schools are found near the heavily populated fault line. (See:
DepEd: School buildings to be graded for quake safety) To pinpoint the distance of a proposed building from the fault line, the Phivolcs has developed a location map of the country’s earthquake faults, according to Ma. Mylene Villegas, Phivolcs Chief Science Research Specialist. Phivolcs has set up a five-meter buffer zone on both sides of the fault line to guide property developers in their construction projects, Villegas said.