Is Metro Manila prepared for a major earthquake?

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.

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. "Developers and design or structural engineers must consult Phivolcs to know how far an active fault is from the planned property. This is [Standard Operating Procedure] for engineers," Abinales says. [See: DPWH exec: Socialized housing units may be prone to quake damage] However, he adds that such decisions still rest on property owners, and permits from local government units (LGUs) do not include such risks. “Building inspections from LGUs only cover the building design, not the location," he said. “Ultimately, there will be no liability on the part of the owner. But still, the risk [from building a structure directly on top of a fault line] is there," Abinales says. Like cooked pasta With deaths from earthquakes often caused by the collapse of buildings, the strict observance of quality control in the construction and maintenance of structures is imperative. “It is very difficult to build a structure that will completely resist earthquakes because of the very high amount of energy released [during earthquakes]," Lagmay says. He added that the force from a magnitude-7 tremor is equivalent to the detonation of 1,000 atomic bombs of the type that were used in Nagasaki. Maximo Noche, an architecture professor at the University of Sto. Tomas, likens buildings to cooked pasta — the longer the pasta or the higher the building, the more flexible it becomes and "the more it will sway with forces like the wind." Similarly, the shorter the pasta (or the height of a building), the more rigid it is. “In earthquakes around the world, low-rise buildings are damaged more often than high-rise structures," Noche says. He adds that modern high-rise buildings are more resilient to shock forces such as an earthquake. Many high-rise structures in Metro Manila have reinforcements that allow them to "sway" along with seismic movements, and less of a solid structure standing on the ground, he says. (See next page) Another Ondoy? Metro Manila has high stakes in the event of a strong earthquake or any disaster, as it serves as the country’s base of government and commerce. This was evident in the devastation from tropical storm Ondoy (Ketsana) last September, which affected more than five million residents and caused at least P11 billion in damage, according to the National Statistical Coordination Board. However, geologists are quick to add that Metro Manila towns and cities do not share the same risks from earthquake damage, even though the West Valley Fault runs directly through some cities. Lagmay says the bedrock composition of various areas will determine their vulnerability when there are seismic movements.

Metro Manila Earthquake Risk Map. Courtesy of GMA News Research, from the Mines and Geosciences Bureau

The western part of San Mateo, Rizal as well as parts of Valenzula, Quezon City, San Juan, Mandaluyong, Makati, and Parañaque are composed of adobe or hardened ash and are more sturdy when there is an earthquake, says Lagmay. Navotas, Malabon, Caloocan, Manila, Las Piñas, Pateros, Taguig, and Muntinlupa are made up of coastal or river sediments that make them less sturdy, says Lagmay. The nearby areas of Obando, Bulacan; the eastern part of San Mateo, Cainta and Taytay in Rizal; Bacoor and Kawit in Cavite share the same soil composition. Be prepared when it strikes As earthquakes cannot be predicted, the best defense is to be prepared for whatever strikes, wherever it strikes, when it does strike. Since 2007, the MMDA has conducted earthquake preparedness training for thousands of government employees, military personnel, students, LGUs, and private entities as part of its educational campaign. The two-day training consists of lectures and practical exercises designed to equip citizens with the necessary know-how in the event of major tremors, according to MMDA Public Safety Consultant Ramon Santiago. “We teach them about earthquake hazards and how to organize teams to help trapped people, including looking for victims in collapsed structures," Santiago says. The MMDA has also equipped its staff with Disaster Response Tools and Equipment Field Storage Units, which house emergency facilities that are immediately accessible in case of natural calamities such as earthquakes and floods. Meanwhile, the Department of Public Works and Highways (DPWH) sends six teams out to conduct ‘rapid, ocular inspection’ of infrastructure at least three times a week around Metro Manila. “We check a building for big cracks and other signs of damage," said DPWH Assistant Secretary Raul Asis. The DPWH has identified at least 20 structures and several school buildings as unsafe. One of these is the Quirino Grandstand at the Luneta in Manila, which has protruding steel bars from its slabs, Asis said. It will be recommended for retrofit pending consultation with a private structural engineer, he adds. Not ready for the big one Despite these measures, however, Santiago says Metro Manila is not sufficiently ready to deal with strong earthquakes like those that devastated Baguio and Haiti. “No, we are not yet prepared. We should do more, especially the greater public. Everyone will have to learn what to do in case an earthquake does strike… and that includes saving other people," Santiago says. Abinales shares this opinion, saying the key to providing safe structures that can withstand disasters is to consult professionals with ample experience. “I can say that medium to high-rise buildings today are safe, because they are complying with set standards for building construction. It is the [owners of] low-rise buildings, especially the old ones, who must take extra caution," Abinales says. “The principle behind an earthquake-resistant building is that while it may sustain damage during an earthquake, it should not collapse," he adds. The building’s design and the quality of materials used affects its behavior during an earthquake. While Noche said that most materials being used today in the country are approved for earthquake pliability, the pricier hardwood is sturdier as it can stand heavier load. Ruby Towers and Hyatt Terraces Having experienced its share of strong earthquakes, the Philippines could learn from a number of building disasters in the past. In 1968, the magnitude-7.3 Casiguran Quake caused the six-story Ruby Tower in Manila to collapse like a deck of cards, killing 268 people. The building crumbled rapidly due to its irregular construction and design, according to experts. The building was not constructed using reinforced concrete, rendering the structure brittle, according to Noche. Abinales added that the building’s irregular design, which was completely walled on one side but not balanced on the opposite side, led to its quick disintegration. “The walled side was too rigid, but the other side was not, so the earthquake’s force was concentrated on the more brittle side, that’s why it collapsed immediately," he says. In post-earthquake photos of Haiti, Abinales observed that collapsed buildings did not seem to have reinforcements, only pure concrete.

Is your building earthquake-resistant?

Architecture professor Maximo Noche from the University of Sto. Tomas says most property developers have adopted several methods to construct earthquake-resistant buildings. If you live or work in a building, check if the following were installed in the structure’s foundation or upper sections: 1. Base Isolation – According to Noche, this method works by supplying shock absorbers that will significantly reduce a tremor’s effect on the building in two ways: * Frictionless rollers that roll freely when the ground shakes, absorbing seismic energy and making the structure above virtually motionless * Flexible pads which resist lateral seismic waves, or the horizontal shaking identified by Phivolcs as the secondary waves of an earthquake, and produce ‘swaying’ motions in the building instead 2. Seismic dampers – Noche explains how this works: “If the earthquake moves to the left direction, the building with dampers moves to the opposite direction with the same amount of energy, thereby canceling it." Many extremely tall buildings use this method, he says.  

“Concrete is a very brittle material. Concrete alone without reinforcements will really result in the crumbling of a building once an earthquake strikes," Abinales says. Noche recommends the use of reinforced concrete, which has metal bars inside, to strengthen structures. [See: ‘Shaking Table’ at Phivolcs helps Pinoys prepare for quakes] The luxury Hyatt Hotel in Baguio City, which was made of concrete, also crumbled in the 1990 earthquake. “The Hyatt Hotel’s design was unusual because it was tilting or terracing," explained Noche. The hotel’s triangular shape rendered the building more vulnerable to ground shaking, Abinales adds. “As much as possible, the structure must be rectangular for it to sway with the movements of the ground," Abinales says. On the other hand, the Casa Vallejo, a wooden hotel on the upper portion of Session Road, was spared. “The Casa Vallejo was only two stories high and was designed to sway with earthquakes," Noche says. But he adds that wooden structures eventually tilt after resisting several earthquakes, and even Casa Vallejo has since undergone renovation to repair its skewed floor. In Manila, one structure that has withstood several earthquakes is the UST main building, the university’s oldest, which remains standing after 87 years even though it sits on the softer and more vulnerable soil of Manila. Noche says the UST was “built in different parts so that it sways in different parts too," and not as a solid mass that is less flexible to varied seismic movements. – YA, GMANews.TV Flash animation by Analyn Perez and layout by Mark Merueñas