Fault system in S. Mindanao possibly to generate higher than M6 earthquake —PHIVOLCS

Marje Pelayo   •   December 17, 2019   •   1578

MANILA, Philippines – The Mindanao region has been experiencing strong ground shaking in the past months.

The most recent was a magnitude 6.9 earthquake on Sunday (December 15) which according to the Philippine Institute of Volcanology and Seismology (PHIVOLCS) was caused by the Tangbulan fault, a 69.2 kilometer stretch that traverses Davao del Sur to Davao Oriental.

According to PHIVOLCS OIC and S&T Undersecretary Renato Solidum, these movements can cause other faults in the region to move as well.

From 1908 to 1970, around five incidents of ground shaking with intensities no stronger than 5 to 8 were experienced across the Davao Region.

The agency noted Southern Mindanao as among the places in the country that sit on multiple fault systems.

The Tangbulan fault alone, the agency explained, can generate up to magnitude 7.2 earthquake.

Towards the east of Tangbulan fault is the Digos fault which can produce up to magnitude 6.3 tremor.

Towards the west is the Makilala-Malungon fault which can generate up to magnitude 7.2 earthquake and is connected to the Cotabato Fault system.

Near the Cotabato fault system lies other faults including the Makilala Fault, Balabag Fault, Matalam Fault, M’lang Fault, North Columbio Fault and the South Columbio Fault.

These faults also can cause ground shaking even stronger than magnitude 6.

The earthquake in October this year, PHIVOLCS noted, was caused by the Cotabato Fault System.

The agency is now closely monitoring the movements of these faults especially those which have been active in the past 10 years.

“Overall sa Mindanao, itong Cotabato-Davao del Sur area ay isa sa rehiyon na walang masyadong malakas na earthquake (Overall in Mindanao, this Cotabato-Davao del Sur stretch is one area in the region that produces small earthquakes),” Solidum said.

“Ibig sabihin may fault, naiipon ang energy, and at some point magbibigay ito, ipapakawala niya ang energy kung kumilos ang fault. So mga strong to major earthquakes ang kaya niya (This means, these faults are generating energy and at some point, it will eventually release this energy when the fault moves. That time, they can produce strong to major earthquakes),” the official added.

Aside from structural damages, PHIVOLCS also warns of possible landslide due to aftershocks or strong rains in mountainous areas where cracks are already visible because of the previous ground shaking. MNP (with details from Rey Pelayo)

Phivolcs lowers Taal Volcano alert to level 1

UNTV News   •   March 19, 2020

MANILA, Philippines – The Philippine Institute of Volcanology and Seismology (Phivolcs) on Thursday said it has downgraded the alert on Taal Volcano to level 1 following the decrease in volcanic quakes and surface activity at the main crater.

In its bulletin, Phivolcs said the Taal Volcano’s condition in the succeeding four weeks after its alert was lowered to level 2, has been characterized by low-level volcanic earthquake activity, stabilizing ground deformation of the Taal Caldera and the Taal Volcano Island edifices, and weak surface activity at the Main Crater and the Daang Kastila fissure.

“DOST-PHIVOLCS is lowering the alert status of Taal Volcano from Alert Level 2 to Alert Level 1 to reflect the overall decreasing trend in the level of monitoring parameters,” its bulletin reads.

State volcanologists said that alert level 1 means that the volcano is still in “abnormal condition,” and that this “should not be interpreted that unrest has ceased or that the threat of an eruption has disappeared.”

Under alert level 1, sudden steam-driven or phreatic explosions, volcanic earthquakes, minor ashfall and lethal accumulations or expulsions of volcanic gas can occur and threaten areas within the Taal Volcano Island.

The alert level may be raised back to alert level 2 “should pronounced change in monitored parameters forewarn of renewed unrest,” Phivolcs said.

The agency reminded residents that entry to Taal’s permanent danger zone, especially the vicinities of the Main Crater and the Daang Kastila fissure, remains strictly prohibited. 

The Taal Volcano was placed under alert level 4 when it spewed ash on January 12 which sent thousands of residents to temporary shelters and disrupted businesses in surrounding areas.

It was later lowered to alert level 2 several weeks later due to decreased unrest. — ROBIE DE GUZMAN

PHIVOLCS may further downgrade alert level over Taal Volcano next week

Marje Pelayo   •   February 21, 2020

MANILA, Philippines – The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported only about 29 volcanic earthquakes around Taal Volcano in the past 24 hours, an indication that rocks underground are breaking.

A column of white steam also continues to form but only up to 50 meters in height.

It has been a week since PHIVOLCS downgraded alert level over the Taal volcano to level 2 from the previous level 3.

According to PHIVOLCS OIC Usec. Renato Solidum, they need to observe Taal volcano’s activities for one more week before they can decide whether to further downgrade the alert status based on the agency’s standard operating procedure.

“Basta tuloy-tuloy ang kanyang mga parametro na bumababa ang bilang pwede natin masabi na pwede nating ibaba ito sa alert level number one (If the parameters continue to reduce in number, we might lower the alert level to number one),” Solidum said.

Entry restrictions remain within the permanent danger zone in Taal Volcano Island.

Solidum said the local government unit needs to assess first if the former residential areas would be conducive for living.

PHIVOLCS does not recommended constructing houses on the volcano island due to the risk of having the ground break apart should the volcano proceed to erupt. MNP (with details from Rey Pelayo)

Magnitude 5.4 quake rattles Davao Occidental

Robie de Guzman   •   February 20, 2020

MANILA, Philippines – A magnitude 5.4 earthquake rattled parts of Davao Occidental on Thursday afternoon, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported.

In its bulletin, Phivolcs said the epicenter of the quake that struck around 5:54 p.m. was traced 35 kilometers southeast of Jose Abad Santos in Davao Occidental.

It had a depth of 190 kilometers and tectonic in origin.

The tremor was felt at intensity III in General Santos City, Tupi and Polomolok in South Cotabato, and Alabel, Saranggani; intensity II in Maasin and Malapatan, Sarangani, and Davao City, while intensity I was felt in Tampakan, South Cotabato.

Phivolcs said there was no reported damage but aftershocks should be expected.

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