Mapping "blind" fault lines
MANILA, 17 February 2012 (IRIN) - Philippine authorities are scrambling to map out previously unknown fault lines across the archipelago after a powerful 6.9 magnitude quake flattened villages, twisted roads and killed dozens in the country's central island of Negros earlier this month.
Experts believe the quake on 6 February was caused by the movement of a "blind fault line" - or a previously unknown fault line - under a narrow strait between Negros and the island of Cebu, catching disaster response officials by surprise.
They said destruction was massive because many residents in the two Negros towns of Guihulngan and La Libertad had for years unknowingly lived in vulnerable areas - on the mountain sides and at the foot of the slopes where they farmed the fertile land.
"Many of the houses [were] made of light materials, not earthquake proof. The bridges and roads were not as strongly built to withstand a powerful quake and many had for many years ignored warnings against living on the slopes because there had never been quakes in these areas," Benito Ramos, head of the National Disaster Risk Reduction and Management Council (NDRRMC), told IRIN.
"The PHIVOLCS [Philippine Institute of Volcanology and Seismology] is now trying to locate and map these so-called blind faults after this quake," he said.
According to the NDRRMC, over 40 people were killed in the quake, but local officials in Negros say dozens remain missing and are feared dead, after landslides buried entire villages.
PHIVOLCS has, over the years, mapped up about a dozen fault lines nationwide.
But because many of these faults had been under-studied, entire communities had for years built residential areas over them.
Two other known faults are the Manila Bay and Manila Trench fault lines, which could lead to powerful destructions, according to the 2004 Metro Manila Earthquake Reduction Study. [ http://www.ndrrmc.gov.ph/attachments/020_E_SUMMARY_01.PDF ]
"There is now a rush to map up all of these other so-called blind faults - or the small ones that were previously unknown," Ramos said, adding PHIVOLCS has yet to determine how many there are.
The 2004 study concluded that a 7.2 magnitude earthquake resulting from the movement of the Manila Trench, for example, could kill more than 34,000 people, injure 110,000 and damage nearly 15 percent of the city's 170,000 residential buildings.
Metropolitan Manila Development Authority head Francis Tolentino said disaster response training for local officials covering the 17 districts was being improved, while much needed search and rescue equipment will be pre-positioned in areas critical to saving lives, like under bridges, for example.
"We need to train more volunteers [ http://www.irinnews.org/report.aspx?reportid=94710 ] for disaster response," said Tolentino. "We will also train volunteers from the nearby regions, because if a quake strikes Manila, they will be the first responders. We will also boost the number of container vans with emergency and rescue equipment like hydraulic tools and cutting and digging equipment, which we would preposition around Manila."
Ramos said the warnings are not meant to scare the public, but rather empower them in case of a major earthquake. "We don't want a repeat of Negros."
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