By Ramon Efren R. Lazaro
MALOLOS CITY – An environmentalist group in Bulacan, fears that an impending strong earthquake may strike any time after a mild quake was recorded to have emanated from the province.
InterAksyon.com reported that “An earthquake, recorded at magnitude 3.8, shook Bulacan and parts of Metro Manila on Wednesday morning.
“Phivolcs said the quake was felt at Intensity 3 to 4 in Makati , Quezon City , and Pasig . There were no immediate reports of damage. Phivolcs said the quake occurred at about 10:07 a.m. (0207 GMT), with its epicenter 31 kilometers north of Dona Remedios Trinidad town in Bulacan.”
Bro. Martin Francisco, chairperson of the Sagip Sierra Madre Environmental Society Inc. (SSMESI), noted that Angat Dam is located in the municipality of Norzagaray , an adjacent town of Dona Remedios Trinidad .
Francisco said that they are apprehensive that the mild quake might be a predecessor to a bigger and stronger earthquake “Batid naman ng marami na lagi kami sa Sagip Sierra Madre Environmental Society Inc (SSMESI) na nagpapaalala na baka ito na yun Big Bang ng Marikina West Fault Line kung saan ay kaakibat sa kinatatakutan natin ay maapektuhan ang kahinaan ng Angat Dam.”
In April this year, dam experts conducting safety study on the structural integrity of Angat Dam has recommended the immediate rehabilitation of the 44- year old dam and its dyke in Norzagaray, Bulacan after it was found that it was sitting on an earthquake fault line.
On the other hand, based on the draft final report submitted by John Grimston of Tonkin and Taylor International—the group commissioned by the government to conduct study on the structural integrity of Angat Dam in coordination with concerned government line-agencies—it was learned that during construction (of Angat dam), a series of fault traces were identified in the foundation of the main dyke for a distance of approximately 15km upstream of it.
Tonkin and Taylor team submitted findings and key conclusions that “the modelling indicates that the dam break flood wave will not only affect the areas near the Angat River, but spread and occupy vast areas well beyond the Angat River channel, and extend both upstream and downstream into the floodplain of the Pampanga River.’
The group also reported that “in total, there are 20 cities/towns in Bulacan, 7 cities/towns in Pampanga and 3 cities/towns in Metro Manila likely to be affected in a Dam/Dyke failure scenario.
It also said that inundation levels can reach as high as 10-30 meters in some areas of Norzagaray, Bustos and Baliuag, Bulacan due to the initial flood wave resulting from breakage. It may reach as high as 5-10 meters in some areas of Pulilan, Plaridel all the way to Calumpit and Malolos City . It is estimated that 3-5 meter flooding will reach areas of Pampanga (due to the Bustos Dam failure) and the flood plain all the way to Metro Manila. While other areas shall likely experience between 1-5 meters of flooding.
PHIVOLCS also opined that the Western Marikina Valley Fault ( WMVF) should be considered active, and that rupture of the main fault could trigger movement on the splay beneath the dyke of approximately 1 – 2m horizontal and 0.5m vertical.
Experts noted that an earthquake on the Western Marikina Valley Fault could therefore trigger movement on the splay of fault trace mapping undertaken by PHIVOLCS suggests that the West Marikina Valley Fault (WMVF) runs several kilometres to the east of Angat Dam.
In September this year, government disaster response teams and officials from the national, provincial and local government conducted a simultaneous earthquake drill in Calumpit town.
Press statement from the Provincial Public Affairs Office headed by Maricel Cruz said that Bulacan Gov. Wilhelmino Sy Alvarado explained that the earthquake drill was conducted by the National Disaster Risk Reduction Council (NDRRMC) as part of their 3rd quarter nationwide simultaneous earthquake drill for critical infrastructure, like Angat Dam.
The drill was personally supervised by NDRRMC officials led by Usec Eduardo Batac, undersecretary for Civil, Veterans and Reserve Affairs of the Department of National Defense; Usec Benito Ramos, NDRRMC executive director and administrator of the Office of Civil Defense in coordination with the Provincial Government of Bulacan, the PDRRMC and representatives from the National Power Corporation, operator of the Angat Dam hydroelectric power plant.
“It pays to be always alert and ready on any eventuality so that we will not be caught flatfooted when disaster of such magnitude struck,” Alvarado said.
If such an incident occurs, dam officials will activate its emergency action plans and will immediately notify and disseminate information to local government units, concerned agencies and then activate the early warning system and monitor the situation.
The PDRMMC will then facilitate the establishments of command posts that will oversee traffic, security, transport, rescue, fire fighting units and logistic teams