The moderate magnitude 4.8 earthquake that rattled parts of Mindanao Sunday morning was likely a “foreshock" of the 6.1 tremor plotted five kilometers southwest of Magsaysay town in Davao del Sur five hours after.
In an interview over DZRH on Sunday, Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato U. Solidum Jr., said the magnitude 4.8 quake and the 6.1 quake both came from the western plate of the Makilala-Malungon fault.
"The 4.8 magnitude quake was a foreshock of the 6.1 magnitude quake, it occurred earlier, so it's called a foreshock," Solidum said in Filipino.
A magnitude 4.8 earthquake rocked parts of Davao del Sur at 7:28 a.m. on Sunday. At around noon, a magnitude 6.1 tremor was also recorded in the province.
According to the United States Geological Survey, foreshocks are earthquakes that precede larger earthquakes in the same location.
"Maraming dikit-dikit na fault at yung huling malakas na lindol nung December 15, nasa eastern plate ng Makilala-Malungon fault ang kumilos. Hindi pa nagtatapos yung serye ng mga paglindol kasi hindi pa naubos yung enerhiya na naipon doon sa fault na yun (Faults in Mindanao are really close to each other and the last strong earthquake on December 15 occurred at the eastern plate of the Makilala-Malungon. The series of earthquakes are not yet over because there's still a lot of energy coming from that fault)," Solidum said.
"Distinct earthquake ito na galing dun sa western plate ng Makilala-Malungon. Nung October 2019, maraming kumilos, yung Tulungan fault, M'lang fault, Makilala fault, yung apat na sunud-sunod nung October, nung December 2019, yung isang bahagi ng Makilala-Malungon yung kumilos (This is a distinct earthquake that came from the western plate of Makilala-Malungon. The series of earthquakes that were recorded in October 2019 came from the Tulungan fault, M'lang fault, and Makilala fault. Meanwhile the quake that occurred last December 2019 came from the Makilala-Malungon fault)," he added.
On December 15, 2019, a magnitude 6.9 temblor struck Davao del Sur, leaving four persons dead.
The province of Cotabato suffered from three consecutive strong earthquakes in 2019: the first with magnitude 6.3 on October 16, the second with magnitude 6.6 on October 29, and the third with magnitude 6.5 on October 31.
According to Solidum, there are five neighboring faults in Central Mindanao, namely, 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.
"Dyan yung magkakadikit, magkakadugtong na fault, so kung gumalaw yung isa, naitutulak nya yung kabila kaya nagkakasunud-sunod (Those are interconnected faults, so if the other one moves, it can trigger other faults to move as well)," Solidum said.