7.2 quake in Mindanao feared
Makilala-Malungon Fault closely monitored as 4th strong tremor in two weeks strikes
The Philippine Institute of Volcanology and Seimology (Phivolcs) on Friday said that there is a possibility that a 7.2-magnitude earthquake may hit Mindanao should the Makilala-Malungon Fault move.
“Ine-entertain namin lahat ng possibilities sa lahat ng aktibong fault doon. Pero ang pinakamalala nga na scenario is having the Makilala-Malungon
Fault that would move [We are entertaining all possibilities on all active faults there (Mindanao). The worst scenario is the movement of the Makilala-Malungon fault],” said Ishmael Narag, officer-in-charge of the Seismological Observation and Earthquake Prediction Division of Phivolcs, following the 5.5-magnitude quake that hit Davao Occidental Friday morning.
“Based on the length of that fault (Makilala-Malungon) puwede itong mag-generate ng magnitude7.2 earthquake, that’s assuming na magra-rupture itong napakahabang fault na ito [this can generate a magnitude 7.2 earthquake, that’s assuming the very long fault ruptures],” he said.
“Kung ikukumpara natin ito dun sa [magnitude] 6.6, mas matindi siyempre ‘yung pwedeng mangyari [If we compare this the magnitude 6.6, the effect is more powerful]. We are talking about a fault beneath another set of municipalities,” he said.
With the possibility of the “Big One” to strike in Mindanao, Phivolcs is monitoring round-the-clock all the active fault lines in the region to determine what triggers the series of destructive earthquakes that struck North Cotabato in a span of two weeks.
Tremors expected until Christmas
Citing historical data of earthquakes in the country, Narag disclosed that residents in the region may continue to feel tremors until December.
“Kung babasehan natin ‘yung mga nakaraang lindol na naganap dito sa Pilipinas, may tendency na umabot at makaramdam pa ang mga tao, especially doon sa area ng epicenter, ng mga pagyanig until December [If we based it on previous earthquakes, there’s a tendency for the people to experience tremors, especially in the areas near the epicenter, until December].”
5.5-magnitude quake
The latest strong quake to hit Mindanao was the magnitude-5.5 earthquake that struck Davao Occidental at 10:33 a.m. Friday. It followed the 6.3-magnitude quake last Oct. 16, the 6.6 quake last October 29, and the 6.5 quake last October 31, all in Tulunan, North Cotabato.
Phivolcs said the earthquake was plotted 334 kilometers southeast of Sarangani, Davao Occidental. It was tectonic in origin with a depth of 33 kilometers.
Several aftershock, as strong as magnitude 4.5, also struck Mindanao Friday.
Three scenarios
In an interview, Narag said it is still undetermined what exactly caused the three tremors that hit Tulunan in October 16, 29, and 31.
But he enumerated three scenarios that could happened during the events such as the existence of a single fault that caused all the tremors; a fault system; or a series of parallel fault moving together.
Narag said Phivolcs is also looking into previous major earthquakes, including a magnitude-5.6 tremblor in Makilala, North Cotabato, last July that might have been caused by the possible fault system.
“It could be just one fault na gumagalaw (that moved). Certain segments of that fault are moving, so it started, probably yung (magnitude) 5.6, and then it triggered the (magnitude) 6.3 (in October 16), then ‘yung (magnitude) 6.6 (in October 29), and the (magnitude) 6.5 (in October 31),” Narag explained.
“Or it could be a fault system. ‘Yung fault system could be a series of fault doon sa lugar (in the area) of the same direction. They are all independent at nag-ge-generate sila ng kani-kaniyang [and they generate their own] magnitude ng [of] events and probably, one event is loading the other fault, or it could be a series of parallel fault which are magkakatabi na [adjacent]faults na gumagalaw [that moved],” he continued.
Among these possibilities, Narag bared that they are looking into the series of north northwest trending faults that have triggered the tremors.
“Stronger kasi ‘yung belief na there is a series of fault na gumagalaw [There’s a stronger belief that there is a series of faults moving] but they are only interrelated dun sa area ng Cotabato [in the Cotabato area]. So that’s why we are calling it the Cotabato Fault System,” he added.
Phivolcs had earlier stressed that Central Mindanao, which includes Cotabato, is among the seismically active regions in the country because of the presence of several active faults in the area.
These faults include the M’lang Fault, Makilala-Malungon Fault, North Columbio Fault, South Columbio Fault, and the western extension of the Mindanao Fault or the Cotabato-Sindangan Fault.
Cotabato Trench is also a major source of earthquakes which can affect the region, Phivolcs said. (With reports from Zea Capistrano and Martin A. Sadongdong)