Geologists at the Philippine Institute of Volcanology and Seismology (PHIVOLCS) have been observing the movements of crust underneath Luzon in their efforts to predict earthquakes and harmful crustal deformations, PHIVOLCS director Renato Solidum said on Tuesday.

He said they are now working in collaboration with Academia Sinica, the national academy of Taiwan which supports researches in various disciplines, in monitoring the behavior of the West Valley Fault System. In a phone interview, Solidum cited the importance of knowing the movement of the northern and southern segments of the West Valley Fault System, which runs from the Sierra Madre mountains down to Marikina City, relative to the movement of the East Valley Fault System.

“We wanted to find out if the movements of the Valley Fault System are locked or creeping. If it is locked, it means it stores large amount of energy that can generate high magnitude earthquake event,” Solidum told the Manila Bulletin.

The PHIVOLCS head also noted that initial research conducted by geologists revealed that the movement of its West Valley Fault's north segment is locked while the south segment movement has a creeping movement in a significant vertical motion.

He explained that a creeping movement of a valley fault system means that it is releasing energy that can generate low magnitude earthquakes that are indication of crustal deformation in Luzon.

“We already found physical manifestations like cracks and vertical displacement on the grounds in the areas of Taguig, Muntinlupa, and San Pedro using GPS (Global Positioning System),” Soliudum said.

Citing a study in 2004, Solidum said there is a possibility that the Marikina Valley Faultline holding the National Capital Region may produce “a maximum credible earthquake” with an estimate of 7.3 magnitude in the Richter Scale.

National Disaster Coordinating Council (NDCC) executive director Glenn Rabonza said it could result to 33,000 casualties, 114,000 people injured and damage to 38 percent of the 1.3 million structures, or around 2,000 establishments, in Metro Manila.

Solidum said it is scientifically possible for an intensity 9 earthquake to hit Metro Manila since their records showed that the Marikina Valley Faultline moves every 200 to 400 years.

“We are in that interval but that doesn't mean it can happen now. Maybe not in the coming years but it can happen in this lifetime. But it is still best if we are prepared for it, (that's why) we are also looking at the relative movement of the different blocks of fault relative to other faults,” he said.