A former president of the Association of Structural Engineers in the Philippines warned Saturday that more than 48,000 could die in Metro Manila if the so-called Big One—a hypothetical magnitude 7.2 earthquake due to the movement of the West Valley Fault—would hit the capital where nearly 13 million lives.
Also yesterday, five light tremors with magnitudes ranging from 3.9 to 5, hit Surigao del Norte, a day after the province was rocked by a moderate magnitude 5.3 earthquake Friday.
In a radio interview, engineer Adam Abinales said the 2004 Metropolitan Manila Earthquake Impact Reduction Study must be updated.
The study warned a magnitude 7.2 earthquake could cause 34,000 to 48,000 deaths and destroy 40 percent of all residential structures in the capital.
“That 48,000 is a low estimate. The study was conducted in 2004, and you can just imagine how much more structures have been erected in Metro Manila since then,” Abinales said.
The Philippine Institute of Volcanology and Seismology on Thursday warned movement in the Manila Trench under the West Philippine Sea could trigger a magnitude 8 earthquake and result in a tsunami that could affect Zambales, Tarlac, and Pampanga.
READ: Quakes? No worry—Phivolcs
Possibility of tsunami
Such a tsunami could also enter Manila Bay within an hour, said Phivolcs Director Renato Solidum, affecting 2.5 million people, 200 schools and 35 hospitals in Metro Manila.
READ: 8-quake, tsunami warnings hoisted
It was the second dire warning from Phivolcs in as many days.
On Wednesday, Solidum said the West Valley Fault running through six cities in Metro Manila and nearby provinces could move and trigger a magnitude 7.2 earthquake anytime.
Solidum said there were plans to put up a national government center in Clark Air Base in Pampanga so that key operations would continue in case a powerful earthquake or a tsunami would hit Metro Manila.
The warning followed a meeting earlier in the week of civil, environmental and geological experts who underlined the urgency that all structures in the country be climate smart and disaster resilient, a gesture aimed to save lives in the event of a higher magnitude earthquake.
The call was raised at the Climate Smart and Disaster Resilient Asean International Conference at Bayleaf Hotel in response to the magnitude 6.1 tremor that toppled the four-story Chuzon Supermarket in Porac, Pampanga.
READ: Grim scenarios emerge after series of tremors
The earthquake, with epicenter in Castllejos, Zambales, caused major infrastructure damage to Clark International Airport.
Glenn Nagaguas, organizer of the CSDR, highlighted the importance of giving priority areas as embodied in the National Climate Change Action Plan that infrastructure is climate-smart and disaster resilient to save lives.
The group has elevated serious concern about the safety of all high-rise and mid-rise buildings, not only in Metro Manila, where nearly 13 million lives, but also in other major cities in the country, whether those buildings can withstand an even higher magnitude or a stronger earthquake.
Treated rebars
Francis Aldrine Uy, dean of Civil, Environmental and Geological Engineering, cited an instance that a hotel or school could stand more than 300 kph tropical cyclone while stressing the need to install systems like a Universal Structural Health Evaluation and Recording System to monitor buildings in real time during an earthquake.
READ: Post-quake check on buildings begins
In the same conference, the safety of Quenched Tempered or Thermomechanically Treated rebars was discussed, particularly its vulnerability to buildings in case of an earthquake.
QT rebars are said to have a fatal flaw since only the outer skin of the rebar meets the minimum grade, and thus becomes vulnerable, in the event of a major calamity, like an earthquake.
Several international studies cited the disadvantage of using QT steels for high-rise buildings.
Reports said that QT steels were manufactured and sold by big steel mills across Luzon.
A 2016 study in Japan highlights the importance of improving the standards of steel bars.
It concludes, “As for buildings, accompanied by the trend in high rise structures, the strength of steel materials was enhanced, and steel materials excellent in seismic resistance were developed, in which the upper limit of yield ratio and the validation limit of yield strength are specified.”
Pampanga Gov. Lilia Pineda said they were looking for the technical specifications of materials used including steels bars, the mixing of cement and the depth of posts in the construction of the collapsed Chuzon Supermarket.
Meanwhile, disaster authorities officially ended on Saturday the search and rescue operations at ground zero of the Chuzon Supermarket, five days after the 6.1 quake that jolted Central Luzon and nearby provinces.
Authorities declared the close of the search and rescue operations after ascertaining no signs of life had been detected under the rubble.
Pampanga Provincial Police personnel showed on Saturday videos of several days of the search and rescue operations, indicating that all possible corners and floors of the collapsed building were searched and cleared.
At the same time, the National Disaster Risk Reduction and Management Council said the number of missing persons from the collapsed Chuzon Supermarket went down to five from the initially reported 14.
The identities of the missing five are still being validated by authorities, the NDRRMC said.
READ: Big quake and substandard steel threaten Metro Manila towers
