A disaster waiting to happen: West Valley Fault quake

Posted at 07/18/14 1:00 AM

First of 2 parts

Quezon City, Manila most vulnerable to strong quake - Phivolcs

MANILA - As if typhoons and floods were not enough, Metro Manila must also prepare for a strong earthquake that's long overdue.

"It might happen in our lifetime, it might take longer. But the more prudent thing to do is prepare," says Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato Solidum.

The latest estimate of Phivolcs, in partnership with Geosciences Australia under the Risk Analysis Project (RAP), shows Quezon City and Manila will have the highest number of casualties should a magnitude 7.2 quake emanate from the West Valley Fault.

The RAP validates and updates findings of the Metro Manila Earthquake Impact Reduction Study (MMEIRS) undertaken by Japan International Cooperation Agency (JICA), Metropolitan Manila Development Authority (MMDA) and Phivolcs 10 years ago.

It says 5,524 people could die in Quezon City alone, and 23,103 people could be seriously injured. "The number of people who will die is dependent on the number of buildings that will collapse," says Solidum.

In Manila, the figures are slightly lower but no less disturbing: 5,449 people could die and 21,620 could be seriously injured.

The 90-kilometer West Valley Fault runs from the Angat reservoir in Bulacan through Quezon City, Marikina, Pasig, Makati, Taguig, Muntinlupa, Rodriguez Rizal, Cavite and ends in Calamba, Laguna. It has moved four times in the last 1,400 years. The last time it ruptured was about 356 years ago. "It doesn't mean the next one will be 7.2, but it's capable of generating a 7.2 quake," Solidum says.


In all, as many as 37,000 fatalities in Metro Manila and Rizal are projected--that's nearly six times more than the official death toll from Supertyphoon Yolanda.

Serious injuries are expected to run up to 148,000.

"140,000 injured people cannot be accommodated in Metro Manila's hospitals. So what do you do? Construct a lot of hospitals, or make sure houses and buildings are safer so they will not collapse?" Solidum asks.

"The main solution is not merely being ready to respond, but making sure houses and buildings that can collapse are corrected while there's time."


But in Quezon City, over 600 families continue to live right above the West Valley Fault. While many of them are illegal settlers, some of them live in multi-million peso homes in affluent subdivisions.

The lives of those in Barangays Batasan Hills, Commonwealth, Bagong Silangan, Holy Spirit, and Matandang Balara will be most imperiled if the above-mentioned quake scenario occurs, according to an independent study by Earthquake and Megacities Initiative (EMI) which was commissioned by the Quezon City Government.

The study projects 4,713 people will die in these five barangays; 14,707 others could end up seriously injured in Barangays Batasan Hills, Commonwealth, Tandang Sora, Bagong Silangan and Holy Spirit.

The local government says it is already building a relocation site and hopes to evacuate illegal settlers by 2016, an election year. "Nag pre-prepare kami ng resettlement para sa kanila. May mga Bistekville si Mayor na tinatayo, sila yung isa sa mga beneficiary nun," says Disaster Risk Reduction Management Officer Elmo San Diego.

But moving illegal settlers to safer ground is never easy. The houses, although built by government, won't be given away for free.

San Diego says he is equally concerned about moneyed Quezon City residents who live right above or near the West Valley Fault "We're talking of Green Meadows, Blue Ridge, White Plains. Sa may Eastwood City din pero malayo-layo about 200 meters away, pero susceptible sila. Mas malapit sa faultline, mas malakas ang ground shaking," San Diego says.

"Yung private lots ang malaking problema natin dahil pag ayaw nila umalis, wala tayong magagawa," San Diego explains. "Kinausap na namin sila about what they can do if their houses are near the buffer zone. Pero yung nakatayo mismo sa buffer zone, wala kaming maitutulong dun. Dapat umalis na sila."

The buffer zone is five meters on either side of the fault.

EMI's "Hazards, Vulnerability and Risk Assesment" report for Quezon City also identifies five "earthquake hotspots" in the City. It said Barangays Bagumbayan, St. Ignatius, Ugong Norte, Bagong Silangan and Batasan Hills consistently have high risk scores when it comes to combined factors such as impact on population, building collapse and impact on critical facilities like hospitals and fire stations.

Engineer Rannie Ison of the Association of Structural Engineers of the Philippines says it is possible to retrofit structures outside the buffer zone to mitigate the impact of a strong quake.

But it would be extremely dangerous to be in a building or house constructed right above the fault. "There's no way to strengthen it so it won't collapse. It's impossible." he says. "It's dangerous because no one knows exactly when an earthquake will occur."