Sánchez: At fault

Wednesday, February 8, 2012

MY FAULT though is that I love living here in Negros Occidental. I have learned to live with all the faults, both human and natural. Maybe in my own way, I can help induce behavioral changes in human faults through this column.

But nature? Here in the Visayas, we can fault the West Panay Fault, the Southern Samar Lineament, the Central Negros Fault, the Cebu Lineament, and the East Bohol Fault for tectonic earthquakes.

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In fact, we can’t fault this week’s earthquake and aftershocks to a human-induced disaster. There’s no one at fault with except the Philippine Fault System, the inter-related system of faults throughout what is called the Philippine Mobile Belt.

If anything, we are “at fault” for living in the Visayas instead of Palawan, said to be “relatively stable” geologically, according to Mahar Lagmay, a professor of the University of the Philippines National Institute of Geological Sciences.

A fault or fault line is a fracture in the rock within the earth’s crust that is the causal location of most earthquakes. Palawan is also not bordered by any major trench or fault line, nearer the West Philippine Sea area is more stable tectonically. Combined with the continental material, there is little chance for the development of active faults in Palawan.

The question is not our fault-finding here in Negros. We know it’s there and whom to blame, and where the danger lurks. We know it’s going to happen sometime down the road.

The situation could have been worse. The Regional Physical Framework Plan of Region VI warned that “the southwestern and northern tips of Panay and Negros are prone to high intensity earthquakes while the rest of the region can experience ground shaking but in low varying degrees. Hazards posed by earthquakes are ground shaking, liquefaction, landslides, ground rupture and tsunami.”

Bacoleños were fortunate enough to experience the benign side of the recent temblor, more of an earth shaking event that provided us with delicious terror and cheap thrills, but none of the ground ruptures and landslides that hit Negros Oriental. Except for some cracks, there was no news of collapsed buildings.

How prepared are our buildings for a big one? The DOST-Philippine Institute of Volcanology and Seismology and Japan’s National Research Institute for Earth Science and Disaster Prevention determined in a test that Philippine masonry houses that use the required size of concrete hollow blocks and reinforcing bars and meticulous application of mortar can “improve its performance in a magnitude 6.9 earthquake.”

A simulation test of a Filipino house that used a standard 6-inch thick concrete hollow blocks (CHB) with 10 millimeter deformed steel bars as reinforcement spaced at 0.4 meter vertically and 0.6 meter horizontally (or every three layers of CHB) can hold its ground with minor damages when it was subjected to a magnitude 6.9 shock.

That isn’t exactly assuring, if you ask me. Probably 6.9 could be the benchmark, the minimum standard. But what if a whopper of a 7-intensity strikes us? Since the country is smack in the middle of the Pacific ring of fire, the disaster math could fluctuate wildly, as the Japanese people know.

In 1981, the Japanese government adopted “shin-taishin” or New Earthquake Resistant Building Standard Amendment using the 1978 Miyagi Earthquake with a magnitude of 7.4 as a standard. Earthquake resistance was defined as “mid-size earthquakes (magnitude 5~7), where a building should suffer no more than a slight amount of cracks and should continue to function as normal.

Last year, an earthquake that hit Japan raised the stakes to 8.9 magnitude. Not even the well-placed technological schemes of mice and men were able to minimize the damage of an earthquake and tsunami.

So with our building standards geared to mid-size earthquakes, who’s at fault if a 7.9 intensity magnitude similar to the one that hit Luzon in 1990 when buildings and houses are unable to withstand the tremor? Obviously, we’re not ready for the big one.

Please email comments to bqsanc@yahoo.com