Metro Manila (CNN Philippines) — A scientist from the Philippine Institute of Volcanology and Seismology on Tuesday quelled fears that another bigger earthquake will hit the southern city of Surigao soon.
This, even as aftershocks continue to rock Surigao City which experienced a 6.7-magnitude quake on Friday.
“An earthquake higher than 6.7 na puwedeng mangyari [that could happen] — the possibility (of that) is very low already,” PHIVOLCS science research analyst Karl Vincent Soriano told CNN Philippines’ The Source.
“We’re not expecting a larger earthquake coming from the same area for the time being,” he added in a separate phone interview.
The quake which hit Surigao on Friday affected more than 1,700 families and left an estimated ₱112.45 million in infrastucture damage.
Related: At least 8 dead; 202 injured in magnitude 6.7 Surigao quake
Prior to Friday’s quake, PHIVOLCS had made an initial forecast of an earthquake hitting Surigao fault line in the magnitude of 7.4. This magnitude was the same as the last earthquake which hit Surigao in 1879.
Aftershocks to recede in weeks to come
More than 170 aftershocks, with the biggest of up to 4.9 magnitude on Tuesday kept residents in this city with a population of approximately 155,000 on edge.
“Itong mga aftershocks na ito, hindi na siya mas malakas pa doon sa main shock natin na 6.7 (magnitude),” Soriano said.
[Translation: These aftershocks are not going to get stronger than the main shock at 6.7 (magnitude).]
Aftershocks are expected from a quake this large.
“This actually will last (a) few weeks from now… And then it will go down, (its) number will become (smaller) as times go by,” he said.
“It might take a few months…meron pa silang mararamdaman [they’ll still be able to feel it],” Soriano added.
Aftershocks are a result of the earth adjusting to the movement of the fault.
“Kasi ganun yung trend most of the time-talagang bumababa siya kasi yung lupa, or the rocks underneath, kasi nag-aadjust sila… siyempre nagkaroon ng rupture,” Soriano expained.
(Translation: “That’s the trend most of the time — (the number of aftershocks) really go down because the earth, or the rocks underneath, adjust… Since there was a rupture.”)
If an aftershock exceeds Friday’s 6.7 magnitude, then it will be marked as the new “mainshock.” Tremors prior to it will be known as “foreshocks.”
Unfortunately, while scientists can study and estimate how strong earthquakes will be, they cannot pin a specific time for when they will occur.
“Right now, we cannot really predict earthquakes and we cannot tell when it will happen,” Soriano disclosed. “What we do know is… saan ito puwedeng maganap [where these can take place] and we can identify the hazards and… possible scenarios for a particular area.”
Philippine Fault Zone
Soriano noted that the fault movement that caused the quake on Friday comes from the Surigao segment of the Philippine Fault Zone.
The zone is the country’s longest fault, spanning 1,250 kilometers from Mindanao to Northern Luzon.
“It’s a zone and it’s divided into segments,” Soriano explained. “By segment siya kung gumalaw… So hindi siya minsanang gumagalaw nang mahaba (It moves by segment, so it doesn’t move several parts at a time).”
The fault is different from the 100-kilometer West Valley Fault, which cuts through Metro Manila and which scientists say is ripe for movement.
All the 1,250 kilometers of fault line are active, said Soriano, and they cannot predict specifically when the segments will move, thus the rationale for earthquake preparedness.
Intensify information campaign
Soriano maintains that those affected by the Surigao quake should not panic. “Duck, cover, and hold” in the event of aftershocks is the rule.
“And then of course make sure that your building or your house is already structurally sound before you go back [to them],” he added.
The National Disaster Risk Reduction and Management Council’s Office of Civil Defense deputy administrator Kristoffer James Purisima said Tuesday that they will “intensify [their] information campaign” on earthquake preparedness in Metro Manila and throughout the country by partnering with local governments and private organizations.
