Bohol quake won't affect West Valley Fault in Manila — Phivolcs

The Philippine Institute of Volcanology and Seismology (Phivolcs) on Monday belied hoaxes circulating via SMS and social media that the recent deadly magnitude 7.2 earthquake in Central Visayas would trigger the movement of Manila's West Valley Fault System, commonly known as the Marikina Fault.

 

At the Kapihan sa Manila Diamond Hotel, Dr. Ishmael Narag, officer-in charge of the Seismology Division of Phivolcs, urged the public not to be spread false information and instead, learn to understand the science behind earthquakes and other natural calamities.

Listen to experts

"People should always listen to the mandated agencies," he said, adding, "There's a science behind everything that's happening."

 

Former Senator Richard Gordon, chairman of the Philippine Red Cross, supported Narag's statement, saying people should listen to scientists on the matter and avoid rumor mongering.

 

"It doesn't help our country," said Gordon, as he urged people to train themselves to handle any disaster.

 

According to Gordon, people should "predict, plan, prepare, (and) practice" instead of worrying about worst-case scenarios from an earthquake along the Valley Fault.

 

The 6:00 a.m. update of the National Disaster Risk Reduction and Management Council (NDRRMC) on Monday reported that the death toll from the October 15 quake has risen to 186 people. At least 2,193 aftershocks have been recorded, 46 of which had been felt.

 

Phivolcs earlier said movement along what may be a newly-discovered fault line in Bohol may be the source of the October 15 earthquake that rocked Central Visayas.

 

The disaster in Central Visayas, affecting mostly Bohol and Cebu, triggered fears of an impending earthquake along Metro Manila's Valley Fault System, which has an east and west side. 

 

However, Narag explained that movements along fault lines are independent from one another.
 

 

If ever there will be an earthquake along the Valley Fault System, it will not be triggered by the Central Visayas quake, Narag said.

 

However, he admitted that, based on geologic studies, the Valley Fault is definitely "locked and loaded" for a possible movement.

 

Based on data from carbon dating studies, there is movement along the Valley Fault every 200 to 400 years, Narag said.

 

The last movement along the fault was in 1658, he said. 

 

"We're at the point where it is already ripe for another earthquake," he added.

 

Worst-case scenario

 

Citing a 2004 Phivolcs study funded by the Japan International Cooperation Agency (JICA), Narag said a very powerful earthquake of magnitude 7 or higher along the Valley Fault could spell a national crisis for Metro Manila's 13 cities and four municipalities.

 

The study said an earthquake along the Valley Fault System could cause 40 per cent of the residential buildings in Metro Manila to collapse or suffer damage.

 

The casualties from the disaster could reach as high as 34,000 deaths and 114,000 injuries. An additional 18,000 deaths could result from fires triggered by the earthquake, the study said.

 

Narag said Phivolcs has recently updated the earthquake impact study with funding from AusAID.

 

The study, expected to be released soon, takes into consideration the changes in population and number of structures along the Valley Fault System.

 

Better technology

 

Narag said new technologies are helping geologists come up with a better hazard mapping system.

 

He noted that previous maps used a 1:10,000 scale but with new instruments, a 1:5,000 map is now possible with images of higher resolution.

 

"The monitoring and location of small to moderate size earthquakes using seismographs may reveal the general location of new earthquake generators, but the surface mapping of these faults may not be easy since some are completely buried by thick sediments," he said.

 

"Most of the major fault systems with clear surface expressions have been mapped using aerial photography, satellite imagery, and field/ground validation by geologists," he added. — TJD/YA, GMA News