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7.2 EARTHQUAKE IN METRO MANILA

MARIKINA VALLEY Fault

Study paints grim scenario
By ELLALYN DE VERA

Manila, Philippines – Can Metro Manila withstand a 7.2 magnitude earthquake?

A two-year study that culminated in 2004 provides a scenario of the magnitude of destruction that awaits the densely-populated metropolis.

The study, entitled Metro Manila Earthquake Impact Reduction Study (MMEIRS), was conducted by the Japan International Cooperation Agency (JICA), Metropolitan Manila Development Authority (MMDA) and Phivolcs based on the 2000 official statistics of approximately 10 million living in the metro.

The current metro population is estimated at close to 12 million.

Experts have studied numerous earthquake sources in and around Metro Manila, and among these faults, the West Valley Fault System that traverses Sierra Madre mountain range, Marikina City up to Tagaytay City, is considered to have the largest impact on Metro Manila should it generate a large earthquake.

With a magnitude of 7.2, the study found that 170,000 residential houses will collapse, 340,000 residential houses will be partly damaged, 34,000 persons will die, and 114,000 persons will be injured.

In addition, fire will break out and burn approximately 1,710 hectares, at least 18,000 persons will be killed by this secondary disaster, bringing the death toll to 52,000. The study also noted heavy damage in infrastructures and lifelines.

Likewise, the damage analysis results of Metro Manila’s vulnerability showed that the areas of Navotas Bay, Manila North Port, South Eastern Manila City, Central Manila Bay, and Valenzuela-Caloocan South-Quezon west intersection are at high risk for fires.

Meanwhile, areas in North Eastern Quezon City, Western Marikina City, Eastern Pasig City, Muntinlupa-Laguna Bay, and Mandaluyong-Makati City are at risk for building collapse.

It said there will be a difficulty in evacuation in the fringes of Metro Manila, Taguig and Las Pinas, as well as in the areas of Navotas Bay, Manila North Port, South Eastern Manila City, and Central Manila Bay.
Another important information cited that Metro Manila will possibly be separated into four regions following the earthquake.

Jane Punongbayan, supervising science research specialist of the Philippine Institute of Volcanology and Seismology (Phivolcs), said reasons for sectoral separation are intense ground shaking, liquefaction, and ground rupture.

“In a sectoral or regional separation, soil may soften affecting the ground structure, credibility of bridges and roads. At this point, evacuation effors will be difficult because most areas will be isolated when there’s a big earthquake,” Punongbayan explained.

The study pointed out that separation into four regions is summarized as: western part of Metro Manila will be isolated from other parts of Metro Manila by fire and building collapse; northern and southern part of Metro Manila will be separated by building collapse and geographical condition; while all road networks running east-west, which are on the fault will be broken due to the movement.

Likewise, the intersecting area between Mandaluyong and Makati has a high possibility of building collapse, while the Pasig River, which is running through east-west, is naturally disadvantageous on terms of separation.

Other roads running north-south in fault areas will be difficult to use, due to the high number of building collapse.

Punongbayan noted that a master plan for earthquake impact reduction had been established for barangay and city-wide preparedness because at times of disasters, in particular a devastating earthquake, people should seek help from hospitals or fire stations proximate to their area.

A Phivolcs study on the Marikina Valley Fault system located in eastern Metro Manila noted that the fault line is evident starting from Bagong Silangan in Quezon City and extending towards the south.

The fault passes through Loyola Grand Villa Subdivision in Quezon City proceeding southward to Barangay Barangka, Marikina City and assumed to proceed southwards down to Valle Verde Subdivision in Pasig City.

The study roughly estimated that in 200 to 400 years, there will be a possible recurrence interval for large magnitude earthquakes from magnitude 6 to 7 at least along the northern portion of the Marikina Valley Fault.

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