EXPLAINER: Why earthquakes have been striking the Philippines one after another

Local

IF IT feels like the ground has been shaking too often lately, that’s because the Philippines has experienced a string of earthquakes in recent weeks.

From Cebu and Davao to La Union and Zambales, experts say there’s no reason to panic as these quakes are not connected.

According to the Department of Science and Technology–Philippine Institute of Volcanology and Seismology (DOST-Phivolcs), the recent series of tremors was caused by different “earthquake generators” across the country.

This is also a reminder of the Philippines’ highly active seismic landscape. Not connected, just coincidental

“Ang mga lindol po natin, hindi po yan connected,” Phivolcs Director Dr. Teresito Bacolcol said in an interview on ANC.

“Ang nag-generate ng mga lindol natin came from different earthquake generators. Yung sa La Union, it was generated by the Philippine Fault. Over the weekend sa Zambales, it was generated by the Manila Trench. And sa Cebu, it was generated by the Bogo Bay Fault. And yung sa Surigao and Davao were generated by the Philippine Trench,” he explained.

The Philippines, he said, sits atop 180 active fault segments and six active trenches, each capable of producing earthquakes independently.

“We expect that because we have 180 active fault segments and six active trenches, we have the possibility that magkasunod-sunod or even magkasabay-sabay ang paggalaw nila. But no, they are not connected,” Bacolcol said.

Normal seismic activity

The latest magnitude 6.0 earthquake that hit Cebu at 1:06 a.m. on Monday, Oct. 13, was later downgraded to magnitude 5.8 by Phivolcs.

The quake’s epicenter was located 14 kilometers southwest of Bogo City, with shaking felt at Intensity V in Villaba, Leyte, and Intensity IV in several areas, including Cebu City, Danao, Argao, and Talisay.

Despite the noticeable shaking, Phivolcs emphasized that this activity remains within the normal range of the country’s daily seismic behavior.

“Every day, we record around 30 quakes, but most of them are minor and only our instruments detect them,” Bacolcol explained. “Sometimes, medyo dumadami lang ang mga nararamdaman ng tao. Normal ito.”

He added that the ground is constantly releasing stress energy.

“Wala namang nangyayari sa ground. I think normal lang ito — it’s just that may malalakas lang na lindol na mararamdaman ng mga tao. Everything is normal. The earth generates energy, and once the rocks can no longer hold the stress, there’s a quake.”

Why the Philippines shakes often

Phivolcs has repeatedly stressed that the country’s location along the Pacific Ring of Fire, a vast belt of tectonic activity encircling the Pacific Ocean, makes it naturally prone to frequent earthquakes, volcanic eruptions, and tsunamis.

The magnitude 6.9 earthquake in Bogo City on September 30 and the magnitude 7.4 tremor in Davao Oriental on October 10, for instance, were also generated by different seismic sources.

“The Davao quake was caused by the Philippine Trench, while the Cebu quake originated from a local fault system,” Bacolcol earlier said. “Different earthquake generators produce independent events; they are not connected to each other.”

He further explained that unless active faults are geographically close to each other, their movements do not trigger chain reactions.

“Our active faults are not connected with each other unless they are very close to each other. In this case, Cebu and Mindanao are too far apart.”

Centuries of seismic history

The Philippine Trench, Bacolcol noted, has a long record of generating major earthquakes, including those in 1921 (magnitude 7.5), 1929 (7.2), 1952 (7.6), and 1924 (8.3), all from the same seismic zone that produced the Davao quake.

The October 10 tremor struck east of Manay, Davao Oriental, at a depth of 23 kilometers and was slightly downgraded from an initial magnitude of 7.5.

The strongest shaking, at Intensity V, was felt in Davao de Oro, Davao del Norte, and nearby provinces, while weaker shaking (Intensity III to IV) reached as far as Eastern Visayas, Northern Samar, Bohol, Negros Oriental, and Cebu.

Stay prepared, not scared

While back-to-back quakes can be unsettling, Bacolcol assured the public that these are not signs of a bigger, connected seismic event.

“We understand people’s fear and disaster fatigue,” he said. “But these quakes are not connected. Wag matakot, instead, we have to prepare for it. We have to accept the reality that we live in the Pacific Ring of Fire, and every now and then, we will be jolted by earthquakes.”(TGP)