Phivolcs: Higher than magnitude 8.1 quake possible
MANILA, Philippines — An earthquake higher than magnitude 8.1 along the six trenches in the Philippines is possible but when it will happen cannot be determined, the Philippine Institute of Volcanology and Seismology (Phivolcs) said yesterday.
The Philippines has six trenches: the East Luzon Trench, Philippine Trench, Manila Trench, Negros Trench, Sulu Trench and Cotabato Trench.
“When a trench is active, people may experience quakes like what happened last June 8, the source was the Cotabato trench,” Phivolcs Director Teresito Bacolcol told The STAR.
The strongest quake recorded so far was an 8.1 tremor caused by the Cotabato trench on Aug. 17, 1976 which took the lives of 3,000 people due to a tsunami.
Based on the length and depth of the trenches, the six active trenches can cause a quake magnitude 8.0 and above.
Bacolcol said the “maximum credible earthquake” from the Philippine Trench and East Luzon Trough may reach the highest at magnitude 8.5.
It was followed by the Manila Trench magnitude 8.4, Sulu Trench at magnitude 8.3, Negros Trench at magnitude 8.2 and Cotabato Trench at magnitude 8.1.
Despite knowing the “maximum credible earthquake” of each trench, Bacolcol said they cannot predict when or how strong the quake will be. “Nobody can predict when an earthquake can happen or how strong it is but we know that these trenches are active and they are capable of the said maximum credible earthquake,” he said.
Bacolcol reminded the public to know the natural signs of an impending tsunami such as strong shaking on land, lower level of water and thundering sound from the sea.
“With tsunamis, it would only take minutes when the waves would happen, we don’t have time to warn them,” he said. “Even if they perceive just one, they should go to a higher place already.”
Major residential hubs and coastal communities across General Santos City, Sarangani and South Cotabato bore the brunt of the devastating magnitude 7.8 earthquake that struck Mindanao on June 8, as revealed by a preliminary satellite analysis by the Philippine Space Agency (PhilSA).
Visual comparisons of nighttime satellite imagery captured just hours after the quake on June 8 at 1:30 a.m. and June 9 at 1:12 a.m. showed a significant loss of illumination across the most heavily populated and vulnerable coastal areas of the region, PhilSA said.
In General Santos City, PhilSA detected a distinct dimming in Barangays Labangal, Apopong, San Isidro, and City Heights, alongside the critical coastal barangays of Siguel and Tambler.
The space-borne data also captured severe disruptions further south, with a noticeable decrease in nighttime lights observed in the coastal municipalities of Glan and Maasim in Sarangani province.
Beyond the coast, the municipality of Polomolok in South Cotabato registered a distinct drop in illumination in the wake of the powerful tremor.
According to PhilSA, this sudden absence of light serves to pinpoint where the heaviest infrastructure damage, localized power grid failures, and emergency population displacements are concentrated.
In a letter to Trade Secretary Cristina Roque dated June 8, the Philippine Iron and Steel Institute (PISI) called for the immediate implementation of the Philippine National Standard 49:2026 or the updated standard for steel bars for concrete reinforcement.
The new standard removes steel grades that do not meet seismic performance requirements.
PISI said these steel bars are widely used in construction today. – Rainier Allan Ronda, Louella Desiderio
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