Phivolcs: Bukidnon needs active fault study

MALAYBALAY CITY (Bukidnon News Dispatch / 28 November 2011) –There is a need to conduct a geologic study in Bukidnon to confirm if there is an active fault cutting through it following the 5.2 magnitude earthquake in Valencia City and the rest of the province this onth, Desiderio Cabanlit, officer in charge of the Philippine Institute of Volcanology and Seismology (Phivolcs) Davao said.

He told the Bukidnon Sangguniang Panlalawigan last week the damage they found in the post-quake evaluation showed that of a possibly even stronger intensity. But he said it should be subjected to a more in-depth analysis.

He stressed, however, that the recent quakes were tectonic in nature.

“The quakes were not caused by any activity of the (Musuan) Calayo volcano,” he added.

Cabanlit, who was called on motion by Valencia City-based board member Ranulfo Pepito, said the probable fault lines such as the Cabanglasan and the Central Mindanao faults are far from the identified epicenter of the quakes.

He said an active fault study will check if indeed there is an active fault line. They will also dig in areas reported to have cracks for carbon dating to check some indicators.

Cabanlit stressed the importance of the study especially in land use and zoning. He said active fault studies can also help map out other hazards such as ground rupture, liquefaction, and landslide.

He cited a study he made in Agusan del Sur where they found out about a fault line.

“The LGU (local government unit) was very happy because they were supposed to build a project over that fault,” he said.

Provincial board members welcomed the suggestion. Cabanlit asked the provincial board to formalize the request to their national office. Bukidnon provincial Vice Gov.  Jose Ma. R. Zubiri Jr. vowed to pass a resolution supporting the study proposed by the Phivolcs official.

But Cabanlit could determine how long the study would take.

“Our previous study on active faults in Caraga and Southern Mindanao, it lasted for months to a year before result was published. Carbon dating takes time, if there are samples to be dated,” he added.

In response to a query by Pepito on land depressions along the Sayre Highway, Cabanlit clarified that not all depressions are signs of active fault lines and quakes.

Pepito said many Valencia City-based businessmen sold properties in the past over fear the volcano in Musuan, where the Central Mindanao University is located will erupt, taking the cue from the tremors.

“That is why this has to be clarified to possibly avoid the repeat of that,” he added.

Cabanlit said they cited that the epicenter was 25 kilometers southwest of Malaybalay City, but it was not in the city. They mentioned Malaybalay only because their monitoring software has Malaybalay City as reference.

The areas worst affected, he added, were all in Valencia City, Brgy.Poblacion, Purok 20, Purok 20A, and Purok 18.

The Valencia City Disaster Risk Reduction and Management Council reported more than a hundred houses totally and partially damaged by the quake that hit strongest on November 7 early evening.

Cabanlit said most of the houses did not pass through inspection by an engineer and were “poorly built”. He described the construction method as faulty with lack of reinforcement to support concrete building materials.

But he said the real indicator of strength of the quake is in its damage to well-built structures such as the houses of a village councilman and a businessman in Purok 18.

He said in those structures, it was clear the design was not compromised. “But there were on the walls and the floor, with one floor area having an opening of about six inches.

He cited the damages to commercial and government buildings in the city, too. Among those where cracks on the walls were observed is the Integrated Bus Terminal in Hagkol, where the CDRRMC office is located.

The Metro Gold commercial building in downtown Valencia City had all its four columns in the entrance broken. He said the city government ordered the temporary closure of the establishment. As of November 12, Phivolcs reported a total of 153 events of aftershocks were recorded in the area. (Walter I. Balane/Bukidnon News)

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