By Henrylito D. Tacio
On April 3, 2024, a strong earthquake struck Taiwan. Measured at magnitude 7.4, according to the United States Geological Survey (USGS), it was the strongest in about 25 years. Although the epicenter was 18 kilometers south of Hualien City, strong tremors were still felt in the capital Taipei, more than 100 kilometers away.
The said earthquake triggered tsunami alerts earlier in the nearby Japan and the Philippines, which were later retracted.
Two days later, on April 5, a 4.8-magnitude earthquake hit near New York City, which shook buildings up and down the East Coast. The epicenter was in Tewksbury in central New Jersey, about 64 kilometers west of New York City.
Although no major damage was reported, New York Governor Kathy Hochul told Reuters: “This is one of the largest earthquakes on the East Coast in the last century.”
There was no big earthquake in the Philippines at the time, but the Philippine Institute of Volcanology and Seismology (Phivolcs) issued a warning to all Filipinos to be prepared for strong earthquakes up to magnitude 8.2.
“The country is part of the Pacific Ring of Fire, and every now and then we will be jolted by major earthquakes,” Phivolcs director Teresito Bacolcol told Philippine News Agency. “Earthquakes are random events and we should be prepared for these geological hazards.”
Earthquake-prone Philippines
It must be recalled that years earlier, experts were already forecasting that a “Big One” – an earthquake that could have a magnitude of 7.2 or even higher – would hit Metro Manila. Such a tremblor could cause 48,000 fatalities and 24,000 severe injuries.
In addition, infrastructure destruction could lead to widespread power and communication failures, alongside significant economic losses estimated by the World Bank at P2.5 trillion.
The Philippines is the ninth most earthquake-prone country in the world, according to a study by Utility Bidder, an award-winning business energy consultancy based in the United Kingdom.
In 2023 alone, the country endured a total of 518 significant earthquakes. The total, however, was only one-fourth of those experienced by the neighboring country, Indonesia, which recorded 1,941 significant earthquakes last year.
On top of the Philippines, as reported in Inquirer, were the following: Mexico, 1,548; Turkey, 847; Chile, 810; Japan, 780; Syria, 724; Papua New Guinea, 666; and Guatemala, 624. Below the Philippines is Peru with 486.
Earthquakes and Active Faults
An earthquake (also known as a quake, tremor, or tremblor), according to a monograph circulated by 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.”
PhiVolcs, which is under the Department of Science and Technology, is the government agency tasked to do studies on earthquakes that occur throughout the country. To do this, scientists use seismographs, instruments that record the vibrations caused by earthquakes.
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.
So-called faults are breaks or zones of weaknesses in rocks along which displacements had occurred or can occur again. They may extend for hundreds of kilometers downward, even down to the base of the lithosphere. Faults showing signs or documented history of recent displacements are called active faults.
The Philippine Archipelago lies between two major tectonic plates: the Philippine Sea Plate and the Eurasian Plate. “Philippine Sea Plate is moving towards the Philippine Archipelago at the rate of about 7 centimeters every year,” Phivolcs explains. “The Eurasian Plate is being subducted along western side of Luzon and Mindoro at the rate of 3 centimeters per year except on Mindoro and northwest of Zamboanga where collision is taking place.”
At the intersection of the two plates is the Philippine Fault Zone, “which decouples the northwestward motion of the Pacific with the southwestward motion of the Eurasian Plate.” Movements along other active faults are reportedly responsible for the present-day high seismicity of the Philippine Archipelago.
According to Phivolcs, at least 5 earthquakes per day occur in the Philippines. For almost four decades now, the country has been affected by 10 earthquakes with magnitudes greater than 7.0. As such, the possibility of these destructive earthquakes occurring again in the future “is very strong.”
Aftershocks
After an earthquake, aftershocks are likely to follow. In seismology, an aftershock isa smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock.
“Communities should prepare for aftershocks,” Phivolcs urges. In case of another strongly felt earthquake, it is recommended that people protect themselves by doing the “drop, cover, and hold.”
In homes and offices, heavy furniture and appliances should be strapped to the walls, and hanging objects securely fastened to prevent these from causing injuries.
People should be cautious of structures visibly weakened or having signs of damage caused by a strong earthquake event, as these may further be damaged by succeeding earthquakes and injure building occupants.
“It is best to contact the concerned municipal/city engineering office for inspection and advice,” Phivolcs suggests. “Civil engineers from the local government and other organizations are strongly enjoined to inspect buildings and infrastructure to determine their structural integrity and recommend appropriate actions.”
Structurally compromised buildings should not be reoccupied unless certified safe by structural engineers. Slopes should be checked for tension/incipient cracks that may have resulted from the strong ground shaking. – ###
