Earthquakes are like a thief in the night. You don’t know when it will happen and where. Last June 8, the southernmost region of Mindanao experienced a magnitude 7.8 earthquake, which struck offshore with its epicenter situated 32 kilometers west of Maasim, Sarangani.
Secretary Renato U. Solidum, Jr., of the Department of Science and Technology (DOST), emphasized that Metro Manila – home to 14 million people – could potentially face an earthquake of the same magnitude.
In a radio interview, Sec. Solidum clarified that the magnitude 7.8 earthquake is not anticipated to arise from the West Valley Fault. Instead, experts consider a magnitude 7.2 earthquake as the most significant threat, commonly known as “The Big One” in Metro Manila.
Sec. Solidum elaborated that the distinction lies in the fact that the epicenter of the Mindanao earthquake was offshore, which is why only a limited number of areas experienced intense shaking.
“However, had this occurred on land, a greater number of buildings would have collapsed or sustained damage, resulting in a far more perilous situation. Metro Manila has a much higher population density compared to the SOCCSKSARGEN region, which would amplify the severity of the consequences,” he stressed.
SOCCSKSARGEN refers to the provinces South Cotabato, Cotabato, Sultan Kudarat, and Sarangani and General Santos City.
“The big earthquake is certainly coming (in Metro Manila). The question is when? No one can tell. It can happen today, tomorrow, or next year. But certainly, there will be an earthquake,” Emmanuel De Guzman, who was then the United Nations International Strategy for Disaster Reduction advisor for Asia-Pacific, was quoted as saying by the Philippine Daily Inquirer.
A report conducted by the Japan International Cooperation Agency (JICA) indicated that Metro Manila is ill-prepared to handle a 7.2-magnitude earthquake, particularly in light of its current resources and the presence of aging building structures throughout the metropolis.
The “Study for Earthquake Impact Reduction for Metropolitan Manila” conducted between 2002 and 2004 revealed that a 7.2-magnitude earthquake instigated by the West Valley Fault could result in approximately 34,000 fatalities, injure around 114,000 people, partially damage an estimated 340,000 residential buildings, and lead to the collapse of roughly 170,000 homes.
“Fire will break out and burn approximately 1,710 hectares and a total of 18,000 additional people will be killed by this secondary disaster,” the study said, adding that infrastructure and essential services will endure significant damage as well.
However, it is not only those living in Metro Manila who are at risk of experiencing The Big One. The Davao Region may also face a similar disaster, potentially triggered by the newly identified Surigao-Mati fault.
According to the Davao regional office of the Philippine Institute of Volcanology and Seismology (PhiVolcs), the fault line extends from Surigao City to Mati City, covering a distance of 320 kilometers.
A recent study conducted by PhiVolcs revealed that a 7.2 magnitude earthquake struck Compostela Valley in 1893. On April 15, 1924, another earthquake with a magnitude of 8.3 occurred in Sigaboy (now known as Governor Generoso) in Davao Oriental.
Desiderio Cabanlit, a member of the team of PhiVolcs scientists who investigated the Surigao-Mati earthquake fault line, clarified that an earthquake registering 7.2 in intensity that occurred in Compostela Valley would be felt in Davao City “in less than a minute,” with an estimated magnitude of around 7.0.
Forewarned is forearmed, so goes a saying. But most Filipinos don’t seem to mind it at all – until it happens.
The Grolier Encyclopedia says about 6,000 earthquakes are detected throughout the world each year. Of this, 5,500 are either too small or too far from populated areas to be felt directly. Another 450 are felt but caused no damage while 35 cause only minor damage. The remaining 15, however, exact great toll in death and suffering, besides heavily damaging houses, buildings, and other structures.
An earthquake (also known as a quake, tremor, or temblor), according to a monograph circulated by the Phivolcs, “is feeble shaking to violent trembling of the ground produced by the sudden displacement of rocks or rock materials below the earth’s surface.”
The earth has an outermost shell, about 80-kilometer thick, which is solid and rigid. This shell is called lithosphere, which is subdivided into small and large pieces with some pieces large enough to contain continents. These pieces of lithosphere are called tectonic plates.
Because of the country’s geographical location, earthquakes happen every now and then.
“Long before Filipinos settled in this country, earthquake faults were already in place,” Dr. Alfredo Mahar Lagmay, a geologist and executive director of Resilience Institute of the University of the Philippines, was quoted as saying.
“These faults shaped our mountains, gave birth to volcanoes, and nurtured life with warmth from Mother Earth. They are the reason for our land’s existence, and we just can’t make them disappear,” Dr. Lagmay said.
The DOST – which is responsible for the coordination of science and technology-related projects in the country – says three tectonic plates encircle the country: the Philippine Plate in the East; the Eurasian Plate in the West; and the Indo-Australian Plate in the South.
“The existence of several fault lines across the country is a manifestation of the movements of these tectonic plates,” DOST states. Geologists define fault lines as slip-ups or cracks in a volume of rock due to rock-mass movement.
A large fault within the earth’s crust is the result of the movement of tectonic plates. A rapid movement of a fault line may produce powerful energy that can trigger a very strong earthquake, scientists say.
The country has five active fault lines: the Western Philippine Fault, the Eastern Philippine Fault; the South of Mindanao Fault; the Central Philippine Fault; and the West or Marikina Valley Fault.
At least 5 earthquakes per day occur in the Philippines, according to PhiVolcs. For almost four decades now, the country has been affected by 10 earthquakes with magnitude greater than 7.0. As such, the possibility of these destructive earthquakes occurring again in the future “is very strong.”
The destructive effects of earthquakes are due mainly to intense ground shaking or vibration. “Because of severe ground shaking, low and tall buildings, towers and posts may tilt, split, topple or collapse, foundation of roads, railroad tracks and bridges may break, water pipes and other utility installations may get dislocated, dams and similar structures may break and cause flooding, and other forms of mass movement may be generated,” PhiVolcs explains.
Liquefaction, the process where particles of loosely consolidated and water-saturated deposits of fine sand are rearranged into more compact state, can also occur. Liquefaction prone areas can be found in beach zones, sand spits, sand bars, wide coastal plains, deltaic plains, floodplains, and former or existing marshlands and swamplands.
Many strong earthquakes originate along faults that break the earth’s rigid crust. It is called ground rupture, a deformation on the ground that marks the intersection of the fault plane with the earth’s surface.
Landslides, the downward movement of slope materials either slowly or quickly, are most likely to happen. Hilly and mountainous areas, escarpments, steep river banks, sea cliffs and other steep slopes are prone to landslides.
Earthquakes can also cause tsunamis. Tsunami, a Japanese term which means “harbor wave,” happens when large ocean waves are produced when faults shift vertically. “The seismic event displaces the mass of ocean water and creates a train of waves that travel as fast as a jumbo jet toward coastal areas,” Dr. Lagmay said.
Sec. Solidum said that most Filipinos are aware that ground shaking does not kill, it is the collapsed houses, buildings, and infrastructures that kill. “Many of us know that collapsed houses, buildings, and infrastructures often are a result of flawed construction practices – meaning two things: old buildings that no longer meet current standards and the other where new buildings are unfortunately constructed that do not conform to current building standards,” he said.
Sec. Solidum argued that if Filipinos believe and accept that bad construction practices cause collapsed structures during earthquakes, then destruction and death due to the earthquake are preventable. “If bad practices are replaced by good practices,” he stressed.
“Destruction and death due to earthquakes are preventable,” he reiterated. “Let us allow the tools of science to assist us in making earthquake-resilient communities to prevent destruction and death.”
As Maria Elena Paterno wrote in her book Earthquake!: “The only way to avoid disasters caused by earthquakes is to prepare for them.”
