Earthquake swarms may or may not lead to stronger tremors, says PHIVOLCS

An earthquake swarm was observed at the Cotabato Trench before the fatal magnitude 7.8 earthquake on June 8, but the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said the smaller tremors do not conclusively prove they triggered the major Mindanao quake.

“An earthquake swarm may or may not lead to stronger earthquakes. Many earthquake swarms gradually decrease and eventually stop without producing a large earthquake,” PHIVOLCS Director Teresito Bacolcol said in a "24 Oras Weekend" report by JP Soriano on Saturday.

PHIVOLCS said earthquake swarms may also help reduce the likelihood of a major tremor by gradually releasing built-up energy.

“Slowly releasing energy instead of ‘yung one big event na naipon lahat ‘yung energy. Ito, slowly releasing energy,” Bacolcol said.

([The swarm is] slowly releasing energy instead of one massive event where all the energy builds up and is released at once.)

An earthquake swarm refers to a series of consecutive moderate tremors without a clear mainshock, usually ranging from magnitude 4 to 5, according to PHIVOLCS.

“Madalas siya sa isang araw, marami sa isang araw. Nagtatagal siya ng mga araw, linggo, minsan tumatagal pa ng isang taon,” PHIVOLCS Science and Research Analyst Jun Bonita said.

(It can occur frequently, with numerous tremors recorded in a single day. It may last for days, weeks, or in some cases, even up to a year.)

Bacolcol clarified that the swarm did not directly trigger the magnitude 7.8 earthquake, adding that it is more accurate to say both events were part of the broader seismic activity along the Cotabato Trench.

Earthquake swarm in Luzon

Meanwhile, an earthquake swarm has also been recorded in Luzon, particularly near Pangasinan along the Manila Trench.

According to PHIVOLCS, 287 tremors were logged from May 26 to June 26. If the Manila Trench generates a major earthquake, it could affect several provinces in Northern Luzon and may also be felt in Metro Manila.

“Itong Manila Trench, may potential yan na above magnitude eight. Ang scenario diyan, pwedeng mawala lang ‘yan, walang mangyayari, [o] pwedeng may malaki. So hindi natin masasabi talaga,” Bonita said.

(The Manila Trench has the potential to generate a quake above magnitude 8. The activity may simply stop without incident, or it could lead to a major earthquake. We really cannot tell for sure.)

Given the unpredictable nature of earthquakes, PHIVOLCS reminded the public of the importance of constant preparedness.—Lyjah Tiffany Bonzo/MCG, GMA News