A powerful earthquake on April 22, 2019 cracked roads in Guagua, Pampanga. Photograph by Jonathan Cellona, ABS-CBN News

How strong an earthquake will the "Big One" be? You need to sit down for the answer

The earthquakes in the past few weeks have rattled many, and renewed an intermittently discussed question: is the mother of all tremors about to come?
Joyce Reyes-Aguila | May 02 2019

It all sounds very Hollywood, yet the thought of a large-magnitude earthquake called the “Big One” hitting Metro Manila and parts of the Philippines is a terrifying prospect. The recent string of tremors experienced in different parts of the archipelago has surfaced this idea again, and left many wondering if this is likely happening soon.

A powerful earthquake on April 22, 2019 caused a portion of the 17th century St. Catherine Church in Porac to collapse. Photograph by Jonathan Cellona, ABS-CBN News


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Just how strong will the “Big One” be? “The magnitude of this earthquake is (estimated at) 7.2 based on the length of the West Valley Fault, which is around 100 kilometers long,” Philippine Institute of Volcanology and Seismology (PHIVOLCS) supervising science research specialist and geologist Jeffrey S. Perez tells ANCX. “The whole of Metro Manila, parts of Bulacan, Rizal, Cavite, and Laguna will experience an Intensity-Eight earthquake that is categorized as “Very Destructive.”

Rescuers carry a victim out of the rubble of Chuzon Building in Porac, Pampanga that collapsed during an earthquake on April 22, 2019. Photograph by Jonathan Cellona, ABS-CBN News

A Metro Manila Earthquake Impact Reduction Study (MMEIRS) report Risk Analysis Project in 2013 estimates that the strong quake will result in 31,000 human fatalities. This is apart from 14,000 people who will suffer very serious injuries, an additional 112,000 cases of serious injury, and 385,000 slightly injured. A total floor area of 88,142,000 square meters will be completely collapsed, while 172,924,000 square meters will experience “slight to extensive damage.” In total, the country is expected to experience an estimated economic loss of around P2.269 trillion.

The Philippines has felt strong quakes in the past, including the 1990 Luzon Earthquake where parts of the Philippines experienced a 7.9-magnitude temblor. It resulted in over 1,600 deaths and P10 billion worth of damage to property. In 2013, a 7.2-magnitude earthquake hit Bohol, taking around 93 lives. The province of Negros was also struck by a 6.7 magnitude earthquake a year before, killing more than 50.   

BGC residents stay outside of highrise buildings in Taguig City on April 22, 2019, after an Intensity 6.1 Earthquake was felt in Metro Manila. Photograph by Jonathan Cellona, ABS-CBN News

Are the recent strong earthquakes signs that the “Big One” will happen soon? “(These) are reminders for us that the Philippines is a seismically active region, being part of the Pacific Ring of Fire,” Perez, who is part of the institute’s Geologic Disaster Awareness and Preparedness Division, explains. “In average, the seismic network of the Department of Science and Technology (DOST)-PHIVOLCS records at least 20 earthquakes every day (in the country). 

“Based on paleoseismic studies and historical accounts of earthquakes, the recurrence interval (frequency) of surface-rupturing events like large-magnitude earthquakes along the Valley Fault System is (likely between) 400 to 600 years. The last earthquake attributed to this fault happened in 1658. Another source of earthquakes in Metro Manila is the Manila Trench (an oceanic trough in the Pacific Ocean) that can generate a magnitude 8.2 earthquake. This will result in an Intensity VIII (tremor) and tsunami. Every region or province in the Philippines can experience a large-magnitude earthquake generated by different active faults and trenches.” PHIVOLCS is a service institute of the DOST that is primarily mandated to mitigate disasters that may arise from volcanic eruptions, earthquakes, tsunami and other related geotectonic phenomena.

The Emilio Aguinaldo College along San Marcelino Street in Manila leans on another building following a magnitude 6.1 earthquake that hit parts of Luzon on April 22, 2019. Photograph by Mark Demayo, ABS-CBN News

The geologist reports that both groups, along with the National Disaster Risk Reduction and Management Council (NDRRMC), initiates quarterly National Simultaneous Earthquake Drills (NSED). “It is an opportune time to test the efficiency and usefulness of the preparedness, response and recovery plans of the different stakeholders like local and national government agencies, offices and schools,” Perez says.

According to him, the response to the recent tremors “demonstrates the effectiveness of conducting regular earthquake drills.” He stresses on the importance of taking such drills seriously to provide information on what to do during and after an earthquake. Being equipped with how to react to shaking using the “Duck, Cover, and Hold” practice, depending on where an individual is situated is key to being able to protect oneself.

Zenaide Canlas surveys her house after an earthquake in Porac, Pampanga on April 23, 2019. The intensity 6.1 quake, which also affected Metro Manila and nearby provinces, destroyed several concrete houses in Porac and affected 500 families. Photograph by Jonathan Cellona, ABS-CBN News

“The recent earthquakes remind us of the importance of community and family preparedness,” adds Perez. Inspection of property, and preparation of emergency kits and “Go Bags” containing personal emergency supplies are non-negotiables in earthquake disaster preparedness. It is highly suggested for families to have agreed-upon meeting spots in case they get separated in public places like malls. Provide alternative safe places or contacts among relatives and friends where they can go to or check-in if communication lines are not available.