Phivolcs releases geological impact report on Bohol quake-A A +A
Tuesday, October 29, 2013
MANILA -- The Philippine Institute of Volcanology and Seismology (Phivolcs) released a geological impact report on its website Monday. The report shows the damage caused by the October 15 quake based on their findings from their October 16 to 25 survey.
The magnitude 7.2 quake produced a surface rupture, as the fault that generated the quake, now named as "North Bohol Fault (NBF)," had no surface manifestation before.
"As of this writing, the mapped surface of the NBF is six kilometers long, from Barangay New Anonang in Buenavista to Barangay Napo in Inabanga," Phivolcs said. The state seismological institute will continue to map the fault.
It added, "The longest, continuous individual trace mapped by Phivolcs approximately two kilometers in Barangay Anonang."
The NBF is categorized as a thrust fault or a (reverse) fault wherein the blocks move upward and downward relative to each other.
The NBF shifts upward between two and five meters, varying in different areas.
"Other typical features associated with reverse faulting, such as scallops, bulges and warps, were also observed in the deformation zone, which extended as wide as 30 meters in some places," Phivolcs said.
It added, "Although the Phivolcs has not yet finished mapping the southwest extension of NBF, it is likely that the fault extends toward north of Maribojoc. A sea-ward shift of the high tide mark after the earthquake was observed by the residents in Barangay Punta Cruz, Maribojoc. This shift in high tide mark may imply that Maribojoc is on the upthrown block of the reverse NBF. The Phivolcs measured the shift to be about 50 meters."
Meanwhile, Phivolcs said that the quake's other impact such as ground shaking, liquefaction which means "a process by which water-saturated sediment temporarily loses strength and acts as a fluid, like when you wiggle your toes in the wet sand near the water at the beach" according to the United States Geological Survey, and earthquake-induced landslides will be explained once the report is updated. (SFP/Sunnex)