Remember the #ShakeDril2016 a few weeks ago? That’s just scratching the surface.
By Bernardo Arellano III
Metro Manila sits at the Pacific Ring of Fire, an active geological area of earthquakes and volcanic activities. Around 18 million people live in the metro and its neighboring provinces, making it one of Earth’s most populous cities. It is also the administrative, political, and economic center of the Philippines, and most of the well-documented cultural and historical sites are sitting at the mouth of the Pasig River delta.
I guess that makes Manila very vulnerable to any movement of the earth.
It’s all your fault, Valley Fault!
Recently, PHIVOLCS has published an atlas of the Valley Fault System, which runs under the urban area of 11-18 million people. The said system may produce a destructive 7.2 magnitude earthquake. Any movement from this system may cause casualties of more or less 31,000 people. On top of that, infrastructure damage that may possibly paralyze Manila, and being too “central” may affect the entire country as well.
For cultural sites though, perhaps only a handful are just within few meters away. We read somewhere that the American colonial administration was even aware of its presence back then, hence only a few structures were built (this may need more research though).
Liquefaction: Making the Earth like a big milk shake
Aside from the fault line, some parts of the metro lies on land that is prone to liquefaction. During earthquakes, the soil in these areas act like liquid and may amplify the strength of the tremor more, than in places with hard bedrock.
To quote Wikipedia:
Soil liquefaction describes a phenomenon whereby a saturated or partially saturatedsoil substantially loses strength and stiffnessin response to an applied stress, usuallyearthquake shaking or other sudden change in stress condition, causing it to behave like a liquid.
In 1985, the earthquake of Mexico City destroyed lots of buildings, especially in districts that once were underwater from Lake Texcoco. Geologists, engineers, architects, and other experts point their fingers to liquefaction.
The City of Manila, having the largest concentration of built historic and cultural sites, sits on top of the Pasig River delta — reclaimed over time by urban developments. Geologists believe that the soil beneath a river delta have higher risk of soil liquefaction, therefore elevating the vulnerability not only of the populace that live in it, but also those old structures, unless engineering and/or architectural intervention has been placed to prevent these structures from collapsing.
The city of Manila may be quite far from the fault, but it doesn’t mean it’s spared from any movement from the ground.
We can’t just “shake it off” like Tay-Tay does.
Mapping Manila’s Geological Hazards and Heritage Sites
The event does not only put people of Metro Manila at risk, but also its cultural heritage. Much of the built cultural properties are vulnerable from destruction during an earthquake — even if it’s less than the worst-case 7.2 magnitude tremor.
The method here is getting publicly-accessible data from the government agencies, laid over the map to get the location of these cultural and historical sites, over geological hazards identified.
Combining data from the Valley Fault System Atlas, Liquefaction Susceptibility Map of Metro Manila (2001) (we have to digitize the PDF image of the map since we do not have a digital shapefile of the map) from the Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS), and cultural sites that were mapped and identified in the Philippine Registry of Cultural Property of the National Commission for Culture and the Arts, this map provides a visual perspective of cultural sites that are vulnerable in an event of an earthquake in Metro Manila.
Manila’s Cultural Sites are Pretty Much at Risk, Actually
The data from the cultural agency shows that majority of the declared and marked histo-cultural sites are located on areas with high susceptibility of liquefaction, especially the historic City of Manila itself. Yes, it’s quite distant from the Valley Fault System, but earthquake waves travel. Experts do know how these liquefaction prone areas are dangerous to structures that have not been intervened with quake-resistant technology.
Aside from the fact that this city is one of the densest in population on Earth. Think about it.
Let’s Prepare Then!
This mapping exercise is just scratching the surface. We’ve seen how Bohol’s historic churches came tumbling down. Not only they were landmarks, but also part of the everyday lives of the residents. It had a great impact to Bol-anon’s society and even in tourism. That was a 7.2 magnitude earthquake in a rural area. However, so much scars remained of that event in 2013. What more if it happened in the center of urban Manila?
In the case of Manila, much of its neglected heritage sites are already in danger of being demolished in push for “development.” Another prevailing mindset is that of “anything old isn’t strong anymore” attitude. Hence, these are better left for dead, not realizing that neglecting it places more people in peril.
Hence, the local and national government should help in protecting and preparing these sites from destruction like documentation and intervention, along with experts. Let them assist the private sector and building or house owners on awareness and protecting their properties. Let the academe help disseminate awareness, instead of keeping it at libraries and journals.
Though these are structures that may be replaced and/or restored, neglecting it not only places a lot of people in danger, but also placing our identity and sustainable living at peril.
Bernardo Arellano III is a Cultural Heritage Worker, Advocate, and Geography Student.