Geologists from the Philippine Institute of Volcanology and Seismology (Phivolcs) found “ground zero” or the fault that triggered the devastating magnitude 7.2 earthquake.
The discovery on Monday confirmed the existence of a previously unknown fault in western Bohol.
The Oct. 15 earthquake claimed around 200 lives and caused major infrastructure damage, including Spanish-era churches in Bohol and Cebu.
Immediately after the earthquake, Phivolcs said the tremor was caused by the movement of the East Bohol Fault.
The epicenter, first reported as Carmen town, was later adjusted to the general area between Sagbayan and Catigbian towns in north central Bohol based on the distribution of aftershocks.
Geologists found a 5-kilometer surface rupture that extended from barangay Anonang in Inabanga town to barangay New Anonang in Buenavista town.
“That fault motion caused the earthquake,” Renato Solidum, director of Phivolcs told ABS-CBN News Channel’s Talkback yesterday morning.
The ground rupture pushed the ground upward from two to three meters, cutting through mountains, roads and possibly settlement areas.
Phivolcs teams are still studying the extent of the fault line which could extend 100 kilometers or longer.
Meanwhile, aftershocks recorded by Phivolcs indicate a general distribution from north Bohol to the offshores of Dalaguete, Alcoy and Boljoon towns in southern Cebu.
The data was plotted on a map by Jessie Alaivar Floren, a private Geographic Informatino System expert in Cebu.
Aside from structural damage, residents in southern Cebu towns of Alegria and Badian and Carcar City have complained that ground water turned to “milo” brown.
“The earthquake may have disturbed the clay-limestone land formations in these areas, affecting their water table and underground water channels,” said Jun Lucero, senior geologist of the DENR Mines and Geosciences Bureau (MGB).
Liquefaction
Lucero told Cebu Daily News that they are now checking reports of possible liquefaction in several areas in Cebu and Bohol.
Severe liquefaction could result in the sinking or submersion of lands, he said.
Areas near the river and those reclaimed from the sea are more prone to liquefaction, Lucero said.
Structures in reclaimed areas, he said, should have stronger foundations and must use materials that can withstand strong ground shaking and liquefaction.
There were reports of suspected liquefaction in the Mandaue City abattoir and city jail; in barangay Cotcot in Liloan town and in barangay Canjulao in Lapu-Lapu City. /with Correspondent Michelle Joy L. Padayhag