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Phivolcs: New fault line may have been source of Bohol earthquake

October 16, 2013 10:30pm
Quake-hit Tubigon building shows absence of rebars
Quake-hit Tubigon building shows absence of rebars . The quake-damaged portion of the old Tubigon Presidencia in Bohol on Wednesday, October 16, shows the absence of reinforced steel bars, which was a common construction practice in the olden days. The municipal hall, constructed during the American era, was one of the many old structures in the province, including heritage churches, which were destroyed or damaged by the previous day's magnitude-7.2 earthquake. Gigi Lolarga
The Philippine Institute of Volcanology and Seismology (Phivolcs) said Wednesday that a newly discovered fault may have been the source of the magnitude 7.2 earthquake that rocked Central Visayas Tuesday.
Phivolcs Seismic division officer in charge Ishmael Narag said in a report aired on "24 Oras" that upon closer examination of their data, they learned that quake's real epicenter is located  between the municipality of Catigbian and Sagbayan in Bohol and not in the town of Carmen as the agency earlier said.
The second epicenter is located near several towns in Bohol that have been the most severely affected by the earthquake.
"[Our data suggests that] the source of the earthquake was probably a different fault system that transects Bohol island. Medyo off siya (new fault line) sa trace ng East Bohol fault," he said.
The death toll from the powerful quake that hit Central Visayas had risen to 144 as of 5 p.m. Wednesday, the National Disaster Risk Reduction and Management Council (NDRRMC) said.
State seismologists said the earthquake's force Tuesday morning was the equivalent of 32 Hiroshima atom bombs.
Narag said Phivolcs did not see the new fault line in Bohol earlier despite the occurrence of an earthquake near the new fault line in 1996 because the province's limestone structure made identifying active faults difficult.
"Medyo mahirap makita yung features ng active faults sa Bohol kasi yung province ay predominantly [composed of] limestone. Ang limestone kasi, madaling ma-weather. So nawawala agad yung anumang superficial features that could have suggested the placement of a new fault," he said.
Narag also said state seismologists already raised the possibility that a strong earthquake might occur in the province when they made the Philippines' comprehensive geohazard maps in 2007.
"The hazard maps [present] worst-case scenarios [such as earthquakes] happening there and if you tried to compare that with what happened now, accurate naman yung nakikita doon sa hazard maps," he said.  — XA/ELR/TJD, GMA News
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