THE series of aftershocks in Davao Oriental was part of natural ground readjustments following the magnitude 7.4 earthquake that struck the province on October 10, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.
Phivolcs director Teresito Bacolcol said the tremors originated from the Philippine Trench, one of the country’s active earthquake generators. An aftershock was recorded on Wednesday morning, October 15, offshore Manay town in Davao Oriental.
‘As of 10:00 a.m., we have recorded 1,387 aftershocks, 19 of which were felt by residents,’ Bacolcol said in Filipino during a media forum.
Most of the weaker tremors were felt in Nabunturan, Davao de Oro, while stronger ones reached Manay and Mati City in Davao Oriental, as well as nearby areas in Tandag, Surigao del Sur; Digos, Davao del Sur; Nabunturan, Davao de Oro and parts of South Cotabato and Sarangani.
Bacolcol explained that after a major earthquake, stress accumulated underground is not released all at once.
‘When a fault breaks, other surrounding areas remain stressed and unstable, causing smaller movements that produce aftershocks. These will gradually lessen as the rocks settle into a new balance,’ he said.
‘Aftershocks are usually about one magnitude lower than the main earthquake,’ he added.
Phivolcs reminded residents to avoid staying in houses with visible cracks or structural damage unless these have been cleared by engineers as safe.
Those living in coastal areas were also urged to watch out for natural tsunami warnings, such as strong ground shaking, sudden sea level withdrawal, or a roaring sound from the ocean and to move to higher ground immediately if any of these occur.
Volcanic updates
Phivolcs also reported minor volcanic activities in recent days.
Two ash emissions were observed from Kanlaon Volcano on Wednesday morning, lasting a total of over an hour with plume heights reaching up to 150 meters. The volcano remains under Alert Level 2, indicating moderate unrest.
Taal Volcano, meanwhile, continues to exhibit low-level activity following a minor phreatomagmatic eruption on October 13. Three volcanic earthquakes were recorded within 24 hours, consistent with its Alert Level 1 status.
Mayon and Bulusan Volcanoes also remain under Alert Level 1, signifying slight unrest. The rest of the country’s 24 monitored volcanoes are at Alert Level 0.
Phivolcs reminded the public to stay out of the Taal Volcano Island permanent danger zone due to the ongoing risk of sudden steam-driven or phreatomagmatic eruptions.