Photos courtesy of PHIVOLCS-DOST FB.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) sheds light regarding the ‘Big One’ and the importance of risk reduction and preparation in mitigating its impacts.

When the Earth moves and the ground shakes, the tendency is often toward fear and panic. People forget what to do and run every which way. But there is more to learn about the normalcy of earthquakes, and the key toward facing this phenomenon is risk reduction and preparation. As the lead agency for this, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) aims to understand these events in order to enlighten the public regarding these natural

Established in 1982, PHIVOLCS is the primary agency concerned with volcanic eruption, earthquake and tsunami activity, and other geotectonic phenomena. It is a service institute under the Department of Science and Technology (DOST) mandated to ensure disaster preparedness and mitigate catastrophes resulting from volcanic eruptions, earthquakes, and tsunamis.


Dr. Renato U. Solidum, the Officer-in-Charge of PHIVOLCS, has 35 years of experience with the agency. He also serves as the DOST Undersecretary (Usec.) for Disaster Risk Reduction and Climate Change, where he works to supervise both PHIVOLCS and the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAG-ASA). “The goal is to make sure that both PHIVOLCS and PAGASA are able to provide the public with the best service by having improved systems, integrated projects, and support from other government agencies. It is also our role to operationalize and transfer the technology that can be used by local government units (LGUs) and other sectors of society,” he says.

Last April 22, 2019, the province of Zambales was rocked by a 6.1 magnitude earthquake, which was also strongly felt in Metro Manila. “When the earthquake occurred, when the [geologic] fault moved beneath the mountains, it released energy. That energy travelled and that was what we felt as intensity,” Dr. Solidum explains.

As one tectonic plate passes over another, they slip and bump against each other allowing energy to build up. When the plates move again, this energy is released along the Earth’s crust as seismic waves. The point on the surface where this occurs is called the epicenter. The measure of seismic energy released from the source of an earthquake is called the magnitude, measured by the Richter magnitude scale. It measures the strength or “size” of an earthquake. On the other hand, the severity of the shaking caused by an earthquake, with particular regard to property and human destruction, is called the intensity. Thus, for the 6.1 magnitude earthquake with the epicenter in Zambales last April 22, 2019, the intensity in Manila was around 4 to 5. In areas nearer the epicenter, the intensity was around 6 to 7 with many structures damaged in the neighboring province of Pampanga.

Because of the country’s geographic location, the Philippines has many active faults or cracks in the Earth’s crust, usually forming the boundaries between the Earth’s tectonic plates. The major fault lines are the Western Philippine Fault, the Eastern Philippine Fault, the South of Mindanao Fault, the Central Philippine Fault, and the Marikina Valley Fault System.

Dr. Solidum explains how the tsunami monitors function.

“Mapping of active faults in the Philippines is a major program of PHIVOLCS because this will be the source of earthquake information in the future and we have been setting up a lot of instruments,” Dr. Solidum says.

These instruments, or seismographs, record ground motion when earthquakes occur. The recordings result in graph outputs that are called seismograms, which contain the information about how strong an earthquake was, how long it lasted, and how far away it was.

The Marikina Valley Fault System is considered active because there are small earthquakes occurring along its length and there is evidence that the fault has moved in the last 10,000 years. This we owe to studies by the PHIVOLCS and the United States Geological Survey which studied the vegetation and the different layers of radiocarbon in the 1990s. However, there are also so-called hidden blind faults that do not reach the surface and produce large events.

Owing to the higher number of installed instruments, earthquakes can now be detected earlier with particular regard to the epicenter. The instruments also help in determining the magnitude of earthquakes. With around 100 instruments, the technology of PHIVOLCS is able to detect large magnitude earthquakes, even down to a magnitude 2 on the Richter scale. However, to read even the micro-earthquakes or those not felt or rarely felt, as is done in Japan, around 300 instruments are needed. “The purpose for detecting smaller events is not to monitor the big ones. But perhaps, we can monitor smaller events that might give trends on how a specific fault might be moving in the future. We want to see if there are possible foreshocks,” the PHIVOLCS chief explains.

Foreshocks are mild tremors that precede a larger seismic event; the full sequence of events being foreshock, main shock, and aftershock, which all pertain to a specific fault. “You cannot [analyze] the whole Philippines as [one] big fault line because we have so many faults; we cannot use the earthquake arising from one fault and the earthquake from another fault to conclude that another fault will move because these faults are not physically connected and interrelated,” Dr. Solidum expounds.

“So what we’re trying to do is, for example, on the West Valley fault, where it transects parts of Metro Manila, Bulacan, Rizal, Cavite, Laguna—that is the ‘Big One’ scenario—and we have sensors all over in other provinces to detect that,” he adds. The PHIVOLCS chief likens the movement of the fault to stretching a rubber band, which is pulled and stretched to the point that it might break. PHIVOLCS studies these, and makes predictions based on pattern recognition and evidence of movement.

Despite the utilization of more sensors that allow them to obtain statistics faster, PHIVOLCS still confirms whether the automated computer calculations are correct. “There is still [human] intervention. [But] now, with more sensors, the statistical error can be smaller,” Dr. Solidum assures. “Because the system worked well in terms of knowing where exactly the earthquake is, we wanted to focus on the response of people.”

Dr. Solidum explains the different reactions of low-rise, mid-rise, and high-rise buildings during earthquakes.

In April 25, 2015, a 7.8 magnitude earthquake rocked Nepal with the epicenter near the capital of Kathmandu and Mt. Everest. It resulted in USD10 billion worth of damage to property, almost 9,000 deaths in Nepal and surrounding areas, over 21,000 injured, and 3.5 million homeless. “In 2015, Kathmandu in Nepal was affected by an earthquake due to the movement of a fault in the mountains. That was the earthquake that they were preparing for but they were not done preparing. We hope that the earthquake will not occur yet [here in the Manila] so that we can prepare better,” Dr. Solidum says.

“The earthquake [last April 22, 2019] is like a preview of what can happen. The strength of the shaking felt in Manila is not very far from the potential shaking that we will feel where we cannot stand because of that invested shaking.” A 7.2 magnitude earthquake has a 30-second period of shaking, which can cause heavy damage and massive destruction. With many high rises in the metropolitan area, these buildings will sway even after the ground has stopped shaking. “The consequence is that around 48,000 people may die because of building collapses in Metro Manila, Bulacan, Rizal, Cavite, Laguna and parts of Pampanga,” the PHIVOLCS chief declares.

To prepare for such an event, the first thing that PHIVOLCS advocates is the strengthening of structures in order to reduce the number of potential casualties. Unfortunately, there is a mistaken belief that building low structures or one-storey buildings is acceptable. When the fault produces a seismic wave resulting in an earthquake, the effects on structures vary depending on the weight or height of the building. If it is near, the smaller lower ones will shake more. If the earthquake is far, the mid-rise and higher ones are affected. “Given that the movement of buildings behaves differently depending on the foundation and the newness, if the West Valley fault is the scenario, we have to look at the quality of the residential and mid-rise buildings,” Dr. Solidum explains.

Based on the 2004 Earthquake Impact Reduction Study conducted by PHIVOLCS in coordination with the Japan International Cooperation Agency (JICA) and the Metropolitan Manila Development Authority (MMDA), the report found that around 10 to 13% of residential buildings or those less than 10-storeys, and the 10 to 30-storeys of low-rise to mid-rise buildings will suffer heavy damage or collapse. It also found that only 2% of the high-rise buildings will suffer damage.

“The reason is that shaking is more intense in the lower structures [because of] the quality of construction for the residential buildings; we do not have many engineered buildings,” the PHIVOLCS chief adds. ‘Not engineered buildings’ are those houses that were built simply by masons and carpenters without supervision of civil engineers, and most of these were done without permits. On the other hand, mid-rise buildings or other residential buildings compliant with the National Building Code or Republic Act No. 6541 before may now be outdated. Because buildings also age, they need to be evaluated and updated to code. “First, there are so many buildings that have been built improperly so we have to have a structural audit of buildings by the local government,” Dr. Solidum says, tapping into the role of the LGUs. “The Building Code was revised in 1992 so we must prioritize inspection of pre-1992 buildings. We need to have engineering missions to find these ‘sick’ buildings that need to be ‘cured,’” he adds.

The reason why people panic is because they do not know exactly what to expect, the fear overwhelms the logic of the preparedness.

This is where the LGUs come in, aside from the professional societies and the universities with engineering colleges. To start, the PHIVOLCS-DOST has developed a questionnaire ‘How Safe is Your House?’ which can be downloaded online from their website. Afterwards, if there is a finding that these houses needed to be retrofitted, the government should develop a scheme to shoulder part of the costs. “You’re investing in something to prevent collapse of buildings; you save more lives rather than have more victims, which is more expensive,” the PHIVOLCS chief says.

The second aspect of preparation is the continued drills so people are made aware. Those who practice the earthquake drills seriously perform the appropriate method— the ‘Drop, Cover and Hold’ method—waiting for the shaking to stop before getting out of the building, the building administrators inspecting the structure before allowing the employees back to the building. Those who do not practice instead run or go to various directions in panic.

“The reason people panic is because they do not know exactly what to expect; the fear overwhelms the logic of the preparedness,” Dr. Solidum states. “But high-rise buildings, the feeling on top versus on the ground would be different; because even if the earthquake has stopped moving, the building will be still shaking for quite a while before it would return back to its normal position. So people must be made aware of what to expect and what to do,” he adds.

The third aspect of preparation is geared toward the LGUs, village and condo associations, offices, and even families who must organize and have an evacuation plan. “So that after the earthquake, if there are things that need to be done like first aid, search, suppression of fire, they can do it,” Dr. Solidum explains. “Because, in a massive earthquake event, you cannot expect the government to help you specifically, considering there might be other areas that need priority support. So we need to mobilize our community.”

At the local level, the mayors should order inspection and ensure the city or town hall is sturdy and stable enough to not suffer damage after an earthquake. “There must still be governance after a major disaster; otherwise, it would be chaos,” the DOST Usec. declares. Cooperation with public utilities is also a must to ensure continued supply of water, electricity, and food in the wake of a major event. This is where the Department of Interior and Local Government (DILG) comes in, in monitoring the LGUs to do the structural audit inspection as well as the disaster risk reduction and preparation. However, many LGUs do not have the capacity to conduct structural audits, which is where assistance from the academe and professional organizations come in.

With regard to disaster risk reduction and preparation, locals must be made aware of their seismic risk profiles—see if there is an active fault in the area. Afterwards, assess the level of shaking and resulting liquefaction. For instance, consider whether a landslide or a fire will occur; if there is a coastline, whether a tsunami or flooding will occur. Assess also the surrounding areas, whether there are malls, schools or churches as to the quantity of people in the locality. All of these information must be gathered toward a joint prevention mitigation effort to address the hazards and potential consequences.

PHIVOLCS has been creating a platform gathering all kinds of maps and hazard data that are being coded into a sophisticated system, funded by the DOST, to be shared with other agencies and LGUs for easier data access and ease of doing business. The GeoriskPH Project launched in August 2018 together with the Mines and Geosciences Bureau (MGB), the National Mapping and Resource Information Authority (NAMRIA), the Office of Civil Defense (OCD), and PAGASA to further develop a national database for hazards and risk assessment. Owing to prevalence of smart phones, the Fault Finder app is already available, launched by the DOST-PHIVOLCS in 2016. Before the year ends, they will also launch another app, the Hazard Hunter.

Earthquakes are a common occurrence. There are many fault lines and trenches all over the Philippines that are constantly moving. When these are pushed together, stress builds up and energy or seismic waves are released through the Earth’s crust. As a result, the ground shakes and this is what we feel from the phenomenon of earthquakes.

“Every day, we record 20 earthquakes; every year, 7,000 to 10,000. They can be in Luzon, Visayas, and Mindanao. For one earthquake to occur here and one earthquake to occur there and one earthquake to occur here, no interrelation, no effect on the Valley fault. It is normal,” Dr. Solidum says. Earthquakes that occur in near proximity are seemingly coincidental, but these are also normal. “In a year, there are more small magnitude events than larger ones. So globally, for example, magnitude 7 on the average would be 20.” In the Philippines, magnitude 6 are around five in a year; magnitude 7 once every two, three, or four years.

DROP. COVER. HOLD. People participate in an earthquake drill in Metro Manila.

“We have been saying that the earthquakes do not kill people,” the PHIVOLCS chief states. “It is the collapse of buildings or houses [that kill people].” This is where preparedness and awareness come in. The DOST-PHIVOLCS, in cooperation with LGUs and other government agencies, is tasked with this. With a vision of being a leading global science and technology institution in helping communities be safe and resilient, PHIVOLCS continues its work of providing information and services for warning, disaster preparedness, and mitigation. — MAIELLE MONTAYRE


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