Deep beneath the ground, running beneath the cities of Laguna's "Industrial Belt" from the cities of San Pedro to Calamba, lies what could be a ticking "time bomb."
That "time bomb" is the West Valley Fault line, a 129-kilometer fault that runs from Dona Remedios Trinidad in Bulacan to Calamba City in Laguna.
The rising urbanization of the first five cities in Laguna province had had experts concerned about what might happen should a 7.0-magnitude or higher earthquake strike the West Valley Fault.
And if we look closer at the maps, it would appear that many Lagunenses are in real danger should what the media have dubbed "The Big One" strike the fault.
San Pedro, Biñan especially vulnerable
What's more concerning, according to experts, is that the Laguna section of the West Valley Fault Line runs along – or near – major industrial and residential areas in the province.
The cities of San Pedro and Biñan, in particular, are especially vulnerable to the possibility of a major earthquake due to rapid urbanization and proximity to Metro Manila.
San Pedro City, the "first" major urban area in Laguna after Metro Manila, is considered the fourth densest city in the province, with a population of 326,001 (as of the 2020 national census) squeezed inside the city's 24.05 square kilometers, or the equivalent of 14,000 people per square kilometer.
And this is where the real danger lies.
Residential, industrial complexes
Way back in 2014, Schadow1 Expeditions, a travel and mapping resource website, posted a series of articles on its blog listing down the major industrial, commercial and residential hubs that sit in the proximity of the West Valley Fault line.
In San Pedro City, in particular, the main fault line and smaller faults identified by the Philippine Institute for Volcanology and Seismology (Phivolcs) run under at least 15 residential areas – most of them in the barangays of Calendola, Estrella, G.S.I.S., Magsaysay, San Antonio, San Vicente (including the new barangays of Chrysanthemum, Rosario, Maharlika, and Pacita II), and Sampaguita Village.
In Biñan City, the western portions of the city, which include the barangays of Malamig and San Francisco, lie above the fault line.
Barangay San Francisco, incidentally, is the site of the now expanding Southwoods City, where high-rise condominiums and office spaces are now becoming part of the cityscape.
Other barangays where the West Valley Fault runs under the province include Sto. Domingo in Sta. Rosa City; Casile and Pittland in Cabuyao City; and Canlubang in Calamba City.
An infograph created by Schadow1 in 2017, using maps and other resources provided by government agencies, showed that San Pedro has the highest number of structures built directly under the fault line in Laguna province – 342 houses, eight industrial complexes, four commercial establishments, two warehouses, at least one public area, and 41 "unspecified" structures.
This was followed by Biñan City with 98 houses and two "unspecified" structures located above the fault line.
These numbers may have changed in the last five years due to the rapid growth of residential and commercial complexes in the two cities, as the local governments are focused on bringing even more investment that would translate to more jobs and a construction boom.
Heavy casualties
In the wake of the 7.0 magnitude earthquake that struck Northern Luzon last July 27, experts in government and other concerned organizations have once again raised the issue of the real possibility of “The Big One” striking the West Valley Fault system.
According to Phivolcs, the West Valley Fault system, in theory, is capable of producing “large” earthquakes on its active phases with a magnitude of 7.0 or higher.
And this possibility looms large, as Phivolcs officials pointed out that according to their studies, the West Valley Fault moves roughly every 400 years.
The last major earthquake recorded in this fault system was in 1658, or 357 years ago, which meant that the next big movement could occur within the next 50 years or so.
And should it ever decide to move, experts have predicted a “very grim” scenario for Laguna province as well as for Metro Manila, where the fault runs along the eastern edge of the region.
In April 2019, during a press conference held after a 6.5-magnitude earthquake struck Central Luzon, seismologists have warned that an earthquake of a similar magnitude occurring at the West Valley Fault could, in theory, kill over 40,000 residents, mainly among the subdivisions that run under the fault line.
"The Valley Fault scenario would extend the level of damage and casualties beyond Metro Manila and [through] the software that we are currently using, we were able to evaluate as well the impact in the surrounding provinces. In fact, the casualty count is more than 40,000,” Ismhael Narag, officer-in-charge of the Phivolcs Seismological Observation and Earthquake Prediction Division, said.
Given the statistics provided above, the possibility of heavy casualties and widespread damage to property in Laguna City’s first five cities could loom very large.
This could also mean a major disruption in the province’s – and the country’s – economy as many industrial complexes are now also located in these cities.
Disaster preparedness
The coincidence of the Abra earthquake happening during the observance of the National Disaster Consciousness Month may have spurred local governments in Laguna province to intensify their disaster response programs even further.
In the cities of San Pedro and Biñan, the local government units held their first inter-barangay disaster preparedness competitions where teams from various barangays demonstrate their knowledge and skills in responding to various calamities – earthquakes included. (See related article on page 4.)
In fact, the Abra earthquake occurred during the first day of the competitions, which may have motivated the participants even further to gain more knowledge and skills on disaster response and first aid.
As earthquakes are still impossible to predict with accuracy, and with the continued urbanization of the so-called “Industrial Belt” in Laguna province, it’s becoming clear that the next “best” step for LGUs in the province is to step up its disaster risk reduction and management programs to ensure “minimal” casualties should the feared Big One strike.
"Hindi naman po talaga natin maiiwasan ang mga disaster, be it natural or human-induced, gaya nga po ng 7.0 magnitude na earthquake sa Abra nitong isang araw,” Maria Theresa Escolano, Regional Director of the Office of Civil Defense (OCD) – Calabarzon, said during the awarding ceremonies for San Pedro City's Barangay Rescue Challenge Championship last July 29.
“Pero pwede po natin itong paghandaan, at kung mangyari man po iyon, pwede po nating ma-mitigate o maibsan ang magiging epekto nito. At ang ginagawa po nating Rescue Challenge ay ang sagot po natin diyan."