Phivolcs says, ‘West Valley Fault ripe for strong quake’

The Philippine Institute of Volcanology and Seismology (Phivolcs) recently urged the people living in Metro Manila and nearby provinces ‘to take extra precaution and prepare for the possibility of a massive earthquake if the West Valley Fault moves.’

West Valley Fault (formerly known as Marikina Valley Fault System) is a 90-kilometer-long fault system that passes through various cities and provinces to include Bulacan, Quezon City, Marikina, Pasig, Makati, Taguig, Muntinlupa, Rizal, Cavite, and Laguna.

The warning came after two massive earthquakes recently hit Nepal leaving thousands of fatality. Phivolcs has constantly been warning Filipinos about the possible occurrence in the area since 2013.

Phivolcs director Renato Solidum, said on interview that there is a possibility that the fault line may move sooner than expected as he disclosed that the West Valley Fault moves every 400 to 600 years and its last movement dates back in 1658 which is 357 years ago.

Solidum likened the occurrence to that of Nepal where their geoscientist counterpart discovered that the fault line in the area actively moves every 750 years, the last of which was in 1344.

The Phivolcs chief stressed that while a magnitude 7.8 earthquake hit Nepal in April 25 followed by a magnitude 7.3 earthquake in barely three weeks, the West Valley Fault may cause a 7.2 magnitude earthquake.

Due to the impending threat, all construction projects now follow the National Building Code to lessen the effects of the earthquake.

Based on the National Building Code, all buildings should be able to withstand earthquakes between Intensity 8 to Intensity 10.

In 2013, Phivolcs has estimated that around 33,500 individuals may die and a bulk of around 113,600 may be injured if the West Valley Fault moves.

Solidum cleared, however, that the warning is made not to scare people but to urge them to be more cautious in the eventuality of a strong tremor.

Aside from ground rupture and ground shaking, a strong earthquake could also cause liquefaction, the loosening of soil after an earthquake.

Liquefaction is defined as the process by which sediment that is very wet starts to behave like a liquid. It occurs because of the increased pore pressure and reduced effective stress between solid particles generated by the presence of liquid. It is often caused by severe shaking, especially that associated with earthquakes.