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Understanding the risks of geohazards

100 Years of Earthquakes in the Philippines


 
Urban planner David Garcia explains, in visually arresting terms, why the whole country needs earthquake drills.
 
In the Philippines, how are earthquakes distributed across time and place? With free, open, and accessible data from the website of United States Geological Survey (USGS), the maps below were crafted to show the historical locations of earthquakes of varying magnitudes and depth throughout the past century. In the first map, a bigger and redder dot means that the earthquake was stronger in terms of magnitude, which is a measure of the energy released by the earthquake event. A bigger magnitude, everything else equal, means a stronger earthquake. On the other hand, the second map shows earthquakes according to depth. If a high-magnitude (high energy) earthquake happens deep in the Earth’s crust, its effects might not be felt strongly. However, if an earthquake is weak in magnitude but shallow in depth, then it can be strongly felt.
 
A century in overview
 
Please look more carefully at the map below. Which places have more dots than the others? Which places have less dots? Where are the locations with deeper earthquakes? Where are the locations with higher-magnitude earthquakes? What are the relation of the earthquake locations, depths, and magnitudes with respect to the active faults, trenches, and related features (depicted in violet lines)?

(drag the slider in the middle to compare the maps)



If you want to see a time-lapse view of the earthquakes, then please click this link below. In sixty (60) seconds, it depicts a century or so of Philippine earthquakes from 16 December 1910 until 12 midnight of 30 July 2015:
 
 
There are limits to the data, though, since there was a scarcity of data earlier in the century (early to mid-1900s). Therefore the interactive map should not be interpreted as if there are more earthquakes recently. It might just mean that our capacity to record them has improved. Also, since the earliest record of USGS on Philippine earthquakes was in 1910, we can only conclude using the available data. 100 years (or 115 years to be precise) of earthquake data does not pale in comparison to the Earth’s age, which is more than 4 billion years.
 
Regarding the other data in the map: the country shapefile was an open-format data from the Disaster Response Operations Monitoring and Information Center (DROMIC) of the Department of Social Welfare and Development (DSWD). Lastly, the data on faults, trenches, and other related features were only reprocessed (georeferenced, redigitized) from a PHIVOLCS map in www.foreclosuresphilippines.com because the data was in a closed-format jpeg file; there are limits to the precision of the lines.
 
The human perspective
 
But before being lost in the technicalities, what should this mean for us at the human scale and lifetime? Should we just give up on these drills, proper urban planning, engineering interventions, etc.? Does the map mean that Palawan is safe; and should, as some are jokingly saying, relocate there?
 
There are other hazards in the Philippines: there are storm surges and tsunamis in the coastal areas; flooding on lowlands; liquefaction on wetlands; mass movements (landslide, etc.) on the uplands, etc. Then, there are severe winds that can hit homes regardless of elevation. Oops, let’s not forget subsidence and sea level rise, both of which can be really slow. Such multihazard situation includes Palawan.
 
If it’s hazardous “anywhere”, then does it mean that we’re hopeless? Let’s have a better—and more hopeful—view of things.
 
First, the maps merely indicate exposure to a particular hazard. We must understand the situation in terms of risk. Risk, as a potential loss, is a result of hazard that operates on an exposed population/community, which has a particular level of vulnerability and adaptation. Let’s elaborate:
 
Hazards are earthquakes, surges, landslides, etc. Exposure means people, houses, infrastructure, investments, etc. Vulnerability means the negative socioeconomic conditions of the exposure (poverty, lack of awareness, etc.). Adaptive capacity means our ability to anticipate, recover, change, and respond with respect to risk.
 
When a risk happens, that’s a disaster. 
 
Hence, when you combine hazard, exposure, vulnerability, and adaptation, then you have risk. No exposure means no risk. Low vulnerability, everything else equal, means low risk. High adaptive capacity, everything else equal, means low risk.
 
Even with the same exposure to the same natural hazards, two different communities can experience a disaster differently due to different levels of vulnerability and adaptation.
 
We have yet to do much to educate ourselves to not confuse such concepts. Such convolution of the notions of disaster, risk, hazard, exposure, vulnerability, and adaptation also impairs our capability as a society to respond properly.

Ever-present risk
 
Therefore, let’s be realistic: in the Philippines, there are no completely safe and unsafe areas. There are only places of varying risks. And since it is extremely hard (and costly) in the country to prevent geohazards from happening, we could reduce risk by: (1) reducing exposure (proper site planning, relocation, etc.); (2) reducing vulnerability (poverty reduction, sustainable livelihoods, etc.); and (3) increasing adaptive capacity. Such initiatives will definitely add to the benefits provided by recent activities such as the Metro Manila Shake Drill.
 
What does it mean for us who are anticipating the Valley Fault earthquake? Operational approaches include:
 
(1) reducing exposure by following easements based on the fault line; 
(2) reducing vulnerability by sustainable urban development, or even by making the maps free, open, and accessible so that more people can be educated; and
(3) increasing adaptive capacity by doing more drills; following good building and construction guidelines; and updating our land use and development plans using risk analyses.
 
Therefore, using the map I’d like to point the public to a higher goal. Our task and hope is to help understand how risks and vulnerabilities are created in order for us to create the necessary conditions to reduce them.
 
On a final note, did you know that the Metro Manila Earthquake Impact Reduction Study (MMEIRS), the document on which our current earthquake-related plans are based, was published 11 years ago in 2004? There are concerns that a large number of the high priority plans in the study has not been realized yet. For instance, since 2004 it’s only recent that NCR-wide drills have become more popular. Now that everyone’s interested again, are we supposed to lose another decade before truly reducing risk? — TJD, GMA News
 


 

David Garcia is an urban planner and geographer with the United Nations Human Settlements Programme (UN-Habitat). His work included planning in Haiyan-affected areas in Guiuan, Ormoc, and Tacloban. The opinions in this article does not necessarily reflect those of his agency or of this website.
 
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