At least three strong earthquakes have rocked portions of the Davao Region since Sunday, begging the question: are these precursors to the "big one"?
A magnitude 6.1 tremor struck at Sunday noon six kilometers off Magsaysay town in Davao del Sur just hours after a magnitude 4.8 earthquake hit the same town. On Monday morning, a magnitude 5.7 quake hit 211 kilometers southeast of Governor Generoso in Davao Oriental.
The tremors are just some of the strongest the region has seen in recent years including a magnitude 6.9 tremor that struck on Dec. 15, 2019.
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Why are earthquakes frequent in the region? It's because it is surrounded by several active fault lines, which generates earthquakes, said Philippine Institute of Volcanology and Seismology (Phivolcs) geologist Jeffrey Perez.
"Doon kasi sa area nila maraming sources ng earthquake. Maraming faults na pupwedeng gumalaw at maaring makaapekto sa kanila," Perez told reportr.
"Hindi kami magtataka na uulit uli yung mga lindol dito so ine-expect natin ito kasi mayroon pang mga faults na hindi pa nagiging source ng lindol," he added.
One fault system near the region is the Cotabato Fault System or a family of active faults capable of generating earthquakes as powerful as magnitude 7.2.
Active faults included in this system are the M'lang Fault, Makilala Fault, Balabag Fault, Makilala-Malungon Fault, North Columbio Fault, and South Columbio Fault. The recent powerful quakes were likely to have been caused by the Makilala-Malungon Fault, Perez said.
Is a 'big one' on the horizon?
In recent years, nationwide earthquake drills have been a must in Metro Manila as authorities raised awareness over a possible "big one" or a worst-case scenario of a magnitude 7.2 tremor.
Preparedness is key according to Phivolcs in dealing with earthquakes since no instrument or technology is available yet for scientists to accurately predict its occurrence.
Perez said each region or province in the Philippines should prepare for their own "big one."
"In reality, bawat region, bawat province in the Philippines, mayroon silang big one and sari-sariling earthquake scenario and most probably, it would be a movement along a fault that is capable of generating an intensity eight earthquake," he said.
An intensity eight earthquake, according to Phivolcs, is a "very destructive" tremor that could cause people to find it difficult to stand even outdoors, damage well-built buildings, and destroy bridges.
In the case of the Davao-Cotabato area, active faults capable of generating magnitude 7.2 earthquakes are the Tangbulan Fault which runs a stretch of 69.2 kilometers, and the Makilala-Malungon Fault which is 65.6 kilometers long.
"The longer yung length ng fault, mas mataas yung magnitude na puwede niyang i-generate," Perez said. " Earthquakes are a reminder na pupwedeng maulit muli kasi mayroon pang faults na hindi pa gumagalaw."
Disaster preparedness is key
Should people living near active faults consider moving? Such mindset would mean that the entire country is inhabitable, Perez said as he highlighted that focus should be on disaster preparedness and infrastructure that that takes into account the threat of earthquakes.
Architects and engineers should ensure adherence to the Building Code so as to avoid disastrous consequences of earthquakes on people.
"Ang kailangan natin dito is preparedness. Ang structure na nagfa-follow ng Building Code--ibig sabihin, nag-follow siya ng right design, ng right construction practice, ng right materials--at intensity eight, makaka-survive pa rin yung building," Perez said.
"Kahit na intensity 8 basta huwag ka sa ibabaw ng fault, walang problema," he added.
