STUDENTS inside the UST campus evacuated buildings after a magnitude 5.0 earthquake shook several parts of Luzon, including Metro Manila, on Saturday afternoon, Oct. 11.
According to the Philippine Institute of Volcanology and Seismology (Phivolcs), the tremor’s epicenter was located off Cabangan, Zambales. It was among a string of unrelated earthquakes in the country since Sept. 30.
Why this story matters: As Metro Manila braces for the so-called “Big One,” or a strong and destructive earthquake, experts underscore the importance of preparedness and structural resilience.
- Phivolcs earlier said in an interview with ANC’s Headstart that the likelihood of a major earthquake striking Metro Manila increases as the year 2058 approaches.
Expert’s take: Rainier Amilbahar, a science research analyst from Phivolcs’ Seismological Observation and Earthquake Prediction Division, said living in the “Pacific Ring of Fire” makes the Philippines naturally prone to seismic activity.
- “[Kapag] sasabihing seismic activity, ang Pilipinas naman is nasa earthquake field area or seismically active field area. So mayroon tayong mga seismic activity na nagaganap, but it’s not exactly [always an earthquake],” he said.
- He said the close distance of areas in Metro Manila to the Valley Fault System (VFS) makes it particularly vulnerable to ground shaking and secondary hazards such as liquefaction.
Mapping the hazards: Amilbahar explained that Phivolcs uses “HazardHunterPH,” a web-based tool that simulates potential seismic, volcanic, and hydro-meteorological hazards in specific locations.
- The system allows users to pinpoint a location on a map and generate a report detailing possible hazards and nearby vulnerable facilities.
- “For example, [kapag] itong Valley Fault System ay gagalaw, and we expect the magnitude it can produce, we can simulate it,” Amilbahar said.
- “It produces a narrative of everything that can hit you, with respect to seismic hazards.”
Fault line: According to the Department of Science and Technology (DOST), the VFS is an active fault system with two fault segments: the 10-kilometer (km.) East Valley Fault (EVF) in Rizal and the 100-km long West Valley Fault (WVF) that runs through different cities and towns of Bulacan, Rizal, Metro Manila, Cavite and Laguna.
- The WVF is of particular concern as it can “generate a large earthquake with a magnitude of 7.2 or commonly known as ‘The Big One’ which poses threat to people, livelihood, buildings and infrastructures,” according to the DOST.
Phivolcs’ seismic hazards assessment: Based on Phivolcs’ hazard assessment, Sampaloc — where UST is located — is 9.1 kilometers west of the West Valley Fault. The area is:
- Generally safe from ground rupture, or surface displacement along an active fault trace;
- Prone to ground shaking of Intensity 8, which can significantly affect all structures;
- Highly susceptible to liquefaction, where soil behaves like quicksand during strong shaking; and
- Generally safe from tsunamis, as it is inland.
UST’s structural readiness: Following the 6.1-magnitude quake that struck Metro Manila in 2019, the Civil Engineering Department and Facilities Management Office (FMO) conducted a structural audit of all UST buildings. Former Civil Engineering Department head Rodelio Tiburcio told the Varsitarian the 2019 assessment found no structurally weak buildings on campus.
- There were no fragile buildings on campus, as all were carefully planned and constructed.
- Surface cracks found in the Beato Angelico Building were not “structural defects.”
- The Buenaventura Garcia Paredes, O.P. Building (BGPOP) is built to withstand 10,000 pounds-force per square inch (PSI), indicating its concrete strength.
- With a 3,000-PSI capacity, the Main Building stands as the country’s first earthquake-resistant structure.
- “Kaya ng Main Building na mag-survive. I’m sure of that…[K]apag lumindol, ‘yong building na ‘yon (Main Building), it will act as individual units, which makes the response to earthquake somewhat calibrated to the load that it is carrying, as a smaller unit,” Tiburcio told the Varsitarian.
Factors to consider: Amilbahar emphasized the need to evaluate various risks when assessing vulnerability to seismic hazards.
- Ground shaking and retrofitting: “Are we prone to experience an intensity 7 (ground shaking), which is destructive? If it is, we have to follow the right rule, the National Building Code, lateral cross-loading, structural code of the Philippines,” he said. “Sundin natin sa pagtatayo ng mga ating pamamahay at istraktura. Kung ‘di tayo pasok, mag-retrofit tayo.”
- Liquefaction hazard: “[Kapag] alam natin na prone tayo sa liquefaction, kung magtatayo man tayo ng istraktura, ibabase natin ang design doon sa heating capacity ng lupa.”
- Distance to landslide-prone areas: Amilbahar said that it is important to assess a location’s distance to landslide-prone areas to prepare for any landslides that may occur.
- Fault lines: “Kapag po dinaanan ng fault ‘yong area na tatayuan natin, kasi bawal na bawal magtayo ng structure [sa] may tinatawag na fault. Gamayin po [natin ang] 9 meters to the left to the right, and follow the proper rules and regulations.”
- Distance to shores: “Pag nasa dalampasigan tayo, i-consider natin ang tsunami. So [kapag] may malakas na lindol, baka mag-generate po ng tsunami.”
Myths to debunk: Amilbahar said the common approach of preparing plans only after an earthquake is misguided.
- “Dapat ang mindset natin ano ang dapat nating gawin [habang] hindi pa dumadating ang earthquake para po pagdating nito, wala tayong problema, walang masusugatan, walang guguho, walang babagsak,” he said.
- Amilbahar also said people often panic during an earthquake when the proper response is to “duck, cover, and hold.” However, he explained that this method is only effective if people are in sturdy structures where nothing is falling.
Tsunami risk: He also addressed misconceptions about tsunami warnings, noting that communities near tsunami-generating areas should not rely solely on advisories.
- “Baka puwede hindi na tayong maghintay ng advisory. Five minutes after shaking, darating na ‘yong [tsunami] waves. Parang imposible na makarating agad sa [evacuation area] nang ligtas,” Amilbahar said.
What’s next? Amilbahar emphasized the urgent need for more sensing equipment, particularly given the recent earthquakes across the country. A shortage of such instruments could hinder the determination of the precise location of earthquake epicenters.
- “Kailangan talaga magdagdag pa ng mga instrumento and software. Kailangan mag-update ng mga AI-assisted na software para mas mapabilis pa ‘yung pagbibigay natin ng information.” With reports from Marielle F. Pesa
