The Marikina Valley Fault

“That earthquake will come from the so-called Valley Fault System or the Marikina Valley Fault. This fault runs diagonally east to west for more than 22 kms., from the eastern boundary of the Novaliches Watershed in Quezon City. It passes through Commonwealth Avenue where the Batasan is, down to the beginning of the Marikina River, on to Camp Aguinaldo, where the Armed Forces is based, and White Plains, straight into the middle of Pasig City and Mandaluyong City, right on Pateros and the eastern rim of Makati City, right towards Taguig City, some 2 kms west of the Laguna de Bay shoreline.”

The Marikina Valley Fault

By: Tony Lopez

From August 2002 to March 2004, the Metropolitan Manila Development Authority, Philippine Institute of Volcanology and Seismology, and the Japan International Cooperation Agency (JICA) conducted a study on the impact of an earthquake on the national capital region.

That earthquake will come from the so-called Valley Fault System or the Marikina Valley Fault.

This fault runs diagonally east to west for more than 22 kms., from the eastern boundary of the Novaliches Watershed in Quezon City. It passes through Commonwealth Avenue where the Batasan is, down to the beginning of the Marikina River, on to Camp Aguinaldo, where the Armed Forces is based, and White Plains, straight into the middle of Pasig City and Mandaluyong City, right on Pateros and the eastern rim of Makati City, right towards Taguig City, some 2 kms west of the Laguna de Bay shoreline.

Then the fault continues sporadically toward Tagaytay where it ends, happily. The fault spares New Manila and San Juan.

You can download Valley Fault System from the Phivolcs website, then Google the Metro Manila map with Google Earth. Superimpose the red fault line and you will get exactly where this earthquake source runs through, down to the last house and building and corner, using the fault map’s coordinates.

Marikina is unfairly used to label the fault when in fact, the anomaly should be named after Pasig and Mandaluyong because it cuts the two emerging cities exactly by half, into west and east. It should be called the Marikina-Pasig-Mandaluyong (MPM) fault, not just the Marikina Fault. A young UP geologist then, a certain Dr. Arcilla, named the fault the Marikina Fault and the name has stuck since nobody complained at that time. The fault is now named the Valley Fault System. Still the word “valley” is there and it clearly refers to the Marikina Valley.

Ask Phivolcs what cities, towns, infrastructure, buildings and landmarks are hit by the fault and they won’t tell you. I asked the late Phivolcs Director Dr. Ray Punungbayan to give me the list and he politely declined, for political reasons.

However, earthquakes know no politics, unlike a guided missile.

Anyway the 2004 JICA study was disturbing. An earthquake of 7 magnitude can be expected anytime because the Valley Fault System had moved four times in 1400 years. The fault has not moved since the 17th century. We are now in the 21st century. The fault is overdue to move and that means it could move anytime today or tomorrow or days after, at a magnitude of 7.

According to the JICA study, an earthquake of that magnitude will affect about 40 percent of residential buildings in Metro Manila (170,000 homes will collapse and 340,000 will be damaged) and kill 34,000 people. An additional 18,000 people will die from fires that will spread after the earthquake, for a total casualty of 52,000.

“This human loss, together with properties and economy losses of Metropolitan Manila, will be a national crisis,” the study says.

The study says “active phases of the Valley Faults is [sic: are] approaching. Many research studies indicate that the estimated magnitude will be around 7.0 or more.”

The study notes that the rapid urbanization of Metro Manila has resulted in unsatisfactory infrastructure construction, poor housing condition, highly dense areas and areas characterized by mixed land use and other inappropriate conditions.

“Thus, the potential for natural disaster in Metro Manila is high and the reduction of its vulnerability is a pressing issue for the safety of residents,” the study stresses.

According to the study, Metropolitan Manila will possibly be separated into four regions by the earthquake impact.

The western part of Metropolitan will be isolated from other part of Metro Manila by fire and building collapse.

The northern and southern parts of Metro Manila will be separated by the building collapse and the geographical condition. The intersecting area between Mandaluyong and Makati has a high possibility of building collapse; moreover, Pasig River is running through east-west, which is naturally disadvantageous in terms of separation.

All road networks running east-west that are on the fault will be broken due to the movement. Other roads running north-south in fault areas will be difficult to use, due to the high number of collapsed buildings.

The study proposes 105 measures to develop a national system resistant to earthquake impact, particularly in Metro Manila.

The study also calls for more research and technology development for earthquake impact reduction measures.

Architect Jun Palafox submitted an update of the study to President Aquino in July last year when he took over Malacañang. Last week, Noynoy’s spokesman dismissed Palafox as an “alarmist.”