One of the possible causes of the magnitude 6.9 earthquake that struck Bogo City, Cebu on the evening of Tuesday, September 30, is an offshore fault that had not moved for around 400 years.
This was revealed by Winchelle Sevilla, head of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) Seismology Division, during an interview with ANC on Wednesday, October 1.
According to Sevilla, the earthquake that hit Cebu was indeed powerful based on PHIVOLCS observations.
“Ang magnitude 6.9 ay isang napakalakas na lindol. Kaya nitong mag-generate ng ground shaking na destructive. ‘Yan actually ‘yong ating naobserbahan at base na rin sa mga information na nakarating sa atin, nakita naman po natin sa mga social media, halimbawa. Marami pong mga estruktura ang na-damage at unfortunately meron po tayong mga casualties,” Sevilla explained.
He added that the fault line that may have caused the tremor had been dormant for centuries.
“Itong lugar kung saan nag-occur ‘yong earthquake, kung titingnan natin ‘yong earthquake catalogue natin, at least in the last 400 years, hindi ito nakaka-experience ng ganyan kalakas na earthquake. Ibig sabihin, ‘yong fault na gumalaw, hindi po siya ganon kadalas ang kaniyang paggalaw,” Sevilla said.
He also clarified that smaller quakes had been previously detected in the area, but these were usually weak.
“Mayroon po tayong mga nade-detect na earthquake po dito pero mahihina lamang po ito. Mga magnitude 4 pababa. Usually po, hindi po ito nararamdaman,” he noted.
“So ito pong earthquake na nangyari po dito po malapit sa city of Bogo[…] sa ngayon po, ang tinitingnan po natin ay offshore fault na with in the last 400 years, hindi po siya gumagalaw,” Sevilla emphasized.
“To gather more accurate information on this fault, we will send a quick response team to conduct an on-ground study and confirm which fault actually moved,” he added.
Meanwhile, as of Thursday, official reports confirmed that the death toll from the Cebu earthquake had risen to 72, while 294 individuals were reported injured.