PHIVOLCS logs over 600 aftershocks from Surigao del Sur earthquake

A total of 659 aftershocks have been recorded since the magnitude 7.4 earthquake hit offshore of Hinatuan, Surigao del Sur on Saturday night, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said Sunday.

PHIVOLCS noted that as of 10 a.m., the magnitude of the aftershocks ranged from 1.4 to 6.2.

“We will still be expecting aftershocks few days to few weeks after the main shock. Pero habang tumatagal naman, lumiliit ang number at bumaba ang magnitude,” PHIVOLCS director Teresito Bacolcol said at a press conference.

(We will still be expecting aftershocks a few days to a few weeks after the main shock. But as time goes on, the number and the magnitude decrease.)

He also pointed out that these aftershocks would no longer result in tsunamis.

“Aftershocks are usually one degree lower than the main shock. The main shock is 7.4 [magnitude], we would expect around 6.4 [magnitude] earthquake. It’s not capable of generating a tsunami,” he explained.

The strong earthquake on Saturday evening caused PHIVOLCS to issue a tsunami alert, with the first tsunami waves expected to arrive between 10:37 p.m. and 11:59 p.m.

The tsunami warning was lifted at 3:23 a.m. Sunday.

Bacolcol, however, noted that sea level monitoring stations confirmed the occurrence of tsunami with preliminary wave heights of 0.64 meter in Mawes Island, Hinatuan; 0.18 meter in Lawigan, Bislig City; 0.05 meter in Port of Dapa, Surigao del Norte; and 0.08 meter in Mati, Davao Oriental.

A mother reportedly died in Tagum City, Davao del Norte following the earthquake on Saturday evening.

The woman died after a wall of a collapsed house fell over her. She was rushed to a hospital but was declared dead on arrival, according to a report by Super Radyo Davao's Jaycel Villacorte on Super Radyo dzBB.

Her husband and child also sustained injuries.

Davao quake, West Valley Fault

The PHIVOLCS chief also clarified that the magnitude 7.4 earthquake in Surigao del Sur was not related to the magnitude 6.8 earthquake that jolted Sarangani Island in Davao Occidental on November 17.

“'Yung November 17 earthquake has nothing to do with the earthquake last night. Magkaiba ang generator no’n. The one that generated the earthquake on November 17 was the Cotabato Trench. Kagabi was the Philippine Trench,” Bacolcol said.

(Their generators are different. The one that generated the earthquake on November 17 was the Cotabato Trench. Last night, it was the Philippine Trench.)

He said the Surigao del Sur earthquake also indicated that the Philippine Trench is active, along five other trenches in the country that are all capable of generating light to major earthquakes.

He stressed that the Philippine Trench and Manila Trench could generate earthquakes up to  magnitude 8.2. The Cotabato Trench, meanwhile, could also generate a magnitude 8 quake.

Bacolcol also said that the earthquake was not caused by a “stress transfer” due to the movements from the Cotabato Trench.

“Hindi stress transfer ang nangyari rito. Magkalayo po ‘yan—stress transfer happens only sa faults na magkakalapit just a few kilometers apart. Dito, magkalayo ang Cotabato Trench and Philippine Trench,” he added.

(What happened here was not stress transfer. Stress transfer happens only on faults that are close together or just a few kilometers apart. In this case, the Cotabato Trench and Philippine Trench are far apart from each other.)

According to Bacolcol, the earthquake from the Philippine Trench has no effects on the West Valley Fault as they also have different generators and are apart from one another.

He also said that the earthquake had nothing to do with weather or climate change. — RSJ, GMA Integrated News