‘Not a major earthquake’

According to our top expert on volcanoes and earthquakes, last Monday’s earthquake that rattled a large area of Luzon and lasted for 10 seconds was not a major one.

It seemed longer than 10 seconds to many of us and the magnitude 6.1 reading of the seismologists seemed stronger. That’s because, as Rene Solidum told media reporters, even if the quake was about 10 seconds, skyscrapers in the metropolis swayed for about a minute.

A respected structural engineer I consulted further explained to me that a flexible taller building would continue to “vibrate” until it dissipates the earthquake energy. But there is nothing to worry about because as he and Solidum pointed out, the newer high-rise buildings in Metro Manila are designed to sway and be flexible.

“Sa mga high-rise, kahit tumigil na iyung paggalaw ng lupa, iyung building ay gagalaw pa rin iyan nang matagal kasi mayroong vibration... Parang walis tingting iyan na itinulak mo, minsan ay maggegewang-gewang iyung taas hanggang tumigil s’ya,” Solidum told radio DZMM.

That’s comforting to know because I am now living in a high rise and I was home when the quake struck. I heard some creaking and when the hanging lamp in my study room started to sway, I knew it was an earthquake.

The Phivolcs chief said last Monday’s quake is minor compared to the so-called “Big One”, a hypothetical magnitude-7.2 earthquake along the West Valley Fault.

“This is definitely not a major earthquake,” he said, adding the earthquake was “felt within 100 kilometers” of the epicenter in Zambales.

It may not be a major quake, but over a dozen people were killed as commercial and government buildings were severely damaged in Pampanga.  It also grounded flights at Clark, stopped the MRT and LRT trains on their tracks, and drove terrified locals into the streets in Metro Manila.

It may not be a major earthquake, but we should take it as a warning. As my structural engineer friend pointed out to me, “For an earthquake of M6.1, the kind of damage in Pampanga should not have happened. That’s more expected for M7 and up. There must have been faults in design or construction.”

Structural integrity of buildings must be reconfirmed. Note that the collapsed supermarket in Pampanga isn’t even a high rise. A post mortem of the damaged buildings conducted by credible structural engineers should be done. Are there any building code violations? Are the steel and concrete used up to standard?

My structural engineer friend made a good observation and suggestion:

“Government preparations for ‘The Big One’ is focused only on what to do after the quake. We should also require all buildings (or maybe just all old buildings and even new buildings, say five years old which are 12 stories and up) to have new reviews by competent structural engineers. That may save lives. We’re now just guessing or banking on ‘general assumptions’.

“Why 12 stories? Until about mid-’60s, the Los Angeles Building Code considered reinforced concrete buildings above 13 stories as ‘critical structures’ that need special demonstration of good structural design and integrity.

“Because of the inherent ‘ductility’ of steel structures, they were considered generally more earthquake-resistant than the ‘brittle’ concrete buildings which acquires ‘quasi-ductility’ only through the steel reinforcements in reinforced concrete buildings. That is why low buildings which are not reinforced usually fail or collapse even in minor quakes.”

It is easy to suspect substandard materials were used specially for the damaged buildings Curiously, there are small steel mills in Central Luzon suspected of producing cheaper, but potentially substandard rebars. The steel mills have been discarded in China and resurrected here.

The local city or municipal engineers who were supposed to have supervised and inspected the collapsed or damaged structures should be made to explain. The LGUs are really the weakest link in our government and maybe the most important for public safety.

Those with the final say on building permits and occupancy permits are often not qualified, or corrupt, or both. That’s why even minor quakes result in serious injuries and even death.

But we have to distinguish between “structural damage” and “non-structural damage” like plastering, concrete hollow block walls, cracks at interface between reinforced concrete and masonry walls, etc.

Usually, my structural engineer friend explained, “structural damage” in concrete manifest itself as a “diagonal crack”, or technically called “shear cracks”, while straight line “cracks” are generally non-structural damage or just “separations” or failure of weak materials like mortar plasters.

There are those who will say that Filipinos are just natural risk takers or are forced by economic circumstances to take risks they shouldn’t. But that’s where government should minimize the risks to life that’s accepted by our people as normal.

Public buildings like malls should be subjected to tougher standards. Big public arenas, churches, and marketplaces should be made to strictly comply with building standards appropriate to the location.

In our country where construction short cuts and cheaper substandard materials are used, there must be constant testing of building materials from cement to steel bars. Substandard stocks should be immediately confiscated and discarded.

I know there aren’t too many qualified structural engineers in the country, but we need to get them to organize a certification system of how compliant a building is to safety standards. The public needs a way of knowing what risks they are taking upon entering a building.

One more thing… someone must go to jail for the collapse of that Pampanga supermarket that killed the most number of people last Monday. Who was the structural engineer who signed off on it? Who was the city or municipal engineer who signed the occupancy permit? Who was the contractor who built that building?

Someone must go to jail or our Building Code standards will remain mere suggestions. If we fail to learn lessons from last Monday’s earthquake, we will live to regret it when the next one strikes.

Boo Chanco’s e-mail address is [email protected]. Follow him on Twitter @boochanco