Phivolcs upgrades earthquake to intensity 8 after evaluation

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Tuesday, February 28, 2012

THE Negros earthquake was stronger that it was first reported, said a Philippine Institute of Volcanology and Seismology (Phivolcs) official.

“We had a team who went to the epicenter of the earthquake, in Tayasan and Guihulngan (in Negros Oriental province),” said Ishmael Narag, Phivolcs Seismological Observation and Earthquake Prediction Division officer-in-charge.

“We saw that the area had major effects of the earthquake, so the intensity was raised from 7 to 8,” he added.


Narag was in town to give a lecture to participants of the training and capacity building program on seismic strengthening for master trainers and local builders in the Visayas region at the University of the Philippines Cebu Campus.

The seminar-workshop, with focus on the effect of quakes on school buildings, was conducted through the partnership of UP Diliman Institute of Civil Engineering with Nanyang Technological University (NTU) of Singapore.

Narag explained that intensity is the measurement of the damage brought about by an earthquake while magnitude is the measurement of the energy released following a temblor.


According to the Phivolcs website, intensity level 7, classified as “destructive,” pertains to a situation in which heavy objects or furniture overturn or topple, big church bells ring, and old or poorly built structures suffer considerable damage.

An intensity 8 earthquake, meanwhile, is “very destructive,” in which many well-built buildings are considerably damaged, while concrete dikes and the foundation of bridges are destroyed by ground settling or toppling. There are also numerous landslides, rockfalls in mountainous or hilly areas.

The 6.9-magnitude earthquake struck Tayasan in Negros Oriental at 11:49 a.m. last Feb. 6.

Narag said liquefaction, one of the effects of earthquakes, was observed mostly in lowlands and near river systems.

Another effect is landslides, which can be triggered by quakes as well as incessant rains.

There are also human causes that aggravate or hasten these effects, such as excavation of the slopes, deforestation and mining, said Narag.


Among the mandates of Phivolcs are earthquake monitoring, volcano monitoring, active faults mapping, paleoseismology, and earthquake-related and volcano-related hazards mapping.

Narag said the agency also offers the rapid earthquake damage assessment system (Redas), a software that can model or simulate earthquake hazards such as ground shaking, liquefaction, landslides and tsunami.

He said local government units could enter into a memorandum of agreement with Phivolcs to avail of themselves of the services.

The Redas is a tool for emergency preparedness and for mainstreaming disaster risk reduction into the local development planning.

In Negros Oriental, the Department of Education reported that more than 100 Schools were damaged.

Tos-Chen Pan, NTU Institute of Catastrophe Risk Management professor, said the school buildings have the same design.

He said there should be a different design for school located near fault lines.

Published in the Sun.Star Cebu newspaper on February 28, 2012.

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