Today, many are still deep in post-mortem analysis mode of the come-from-behind win of Argentina against England in their semi-final match earlier this morning in the ongoing World Cup 2026, featuring this “beautiful game” called football, believed to have been brought to Argentinian shores by a Scottish school teacher only in the late 1880s.

Others are glued to their TV monitors and smart phones pursuing the proceedings of the ongoing impeachment trial of Vice President Sara Duterte, either by watching the replays of the court proceedings the past seven days or to press conferences afforded to both the prosecution and the defense parties.

But many may have forgotten that today also marks the 36th anniversary of the deadly magnitude 7.8 earthquake of Northern Luzon that devastated an area not smaller than 20,000 square kilometers from Cabanatuan City in Nueva Ecija, to Baguio City in Benguet, to Dagupan City in Pangasinan.

On July 16, 1990, the earth was shaken with a power roughly equivalent to the energy released by 250 Hiroshima atomic bombs. The energy released was so powerful the earthquake toppled numerous buildings, destroyed bridges and highways, collapsed residential houses, induced numerous landslides especially in mountainous areas, and ground settlement and liquefaction in soft, low-lying and coastal areas. More than 1,500 lives perished and the cost of infrastructure damage in 1990 was estimated at P20 billion, which is about 130 billion pesos in today’s currency equivalent.

The July 16, 1990 earthquake was generated by the 125-kilometer-long Digdig segment of the dreaded Philippine Fault System which traverses the entire length of the Philippine archipelago for about 1,500 kilometers from Bangui in Ilocos Norte in the north, to Mati in Davao Oriental in the south.

In between, the fault traverses the Cordillera Mountains, Southern Sierra Madre, Bondoc Peninsula and Masbate Island in Luzon, the Visayan island of Leyte before it enters into Mindanao in Surigao Del Norte, proceeding southwards Agusan Del Norte and Sur, Davao Del Norte, then Davao De Oro.

In a recent study, Aurelio et al. (2025) showed that the Philippine Fault System has generated more than 60 earthquakes with magnitude 5.0 or greater in the last 50 or so years. This translates to an average of more than one magnitude 5.0 or greater earthquake per year. Around 10 of the 60 or so earthquakes in 50 years are destructive. This translates to an average interval of one destructive Philippine Fault-generated earthquake every 5 years.

Other earthquake generators

But it is not only the Philippine Fault that is capable of generating destructive earthquakes. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) maps more than 200 active faults that transect the country, some of which are as capable as the Philippine Fault in generating magnitude 7- or-greater earthquakes, such as the six subduction trenches that surround the archipelago, including the East Luzon Trough and Philippine Trench in the east, and the Manila, Negros, Sulu and Cotabato.

One such equally strong seismic event was the recent earthquake that devastated Sarangani and South Cotabato provinces on June 8, 2026. With a magnitude of 7.8, the Sarangani earthquake considered by Phivolcs to have been generated by the Cotabato Trench, was as powerful as the July 16, 1990 North Luzon earthquake, although the former caused significantly less infrastructure damage and death toll. This is partly due to the difference in the style of faulting related to the Philippine Fault and the Cotabato Trench, the location of the epicenters, and the depth of focus.

The 1990 Luzon quake struck land, and came from a shallow (around 15 kilometers) focus, thus the more pronounced effect to the surface including a ground surface rupture of more than 100 kilometers. The Sarangani quake of 2026 on the other hand struck offshore, came from a deeper focus (more than 50 kilometers), and no ground surface rupture, hence lesser destructive effect on the surface.

Earthquake parameters

To better understand the capability of an earthquake to inflict damage to the environment, it is important to be aware of three important parameters, namely; the magnitude, the depth of focus, and the location of the epicenter.

Magnitude is measure of the amount of energy released by the earthquake-generating fault – the higher the magnitude, the greater is the generator’s capability to inflict damage. Focus is the depth from which earthquake waves emanate – the shallower the focus, the stronger the shaking at the surface, hence greater damage. This is so because seismic waves lose strength as they travel greater distances.

Epicenter is the projection of the focus at the surface. In general, areas located closer to the epicenter are more vulnerable to damage than those away from it. The amount of shaking of the ground, sometimes referred to as “intensity” generally increases toward the epicenter.

It is important to distinguish “intensity” from “magnitude. ”The distinction is often likened to the difference between the wattage of a lightbulb and the strength of its illumination as one moves away (dimming) or toward (brightening) it. Wattage, like magnitude, is a fixed value, while strength of illumination, like intensity, is a function of distance to the observer. – Rappler.com

Mario A. Aurelio, PhD is a professor at the National Institute of Geological Sciences-University of the Philippines (UP NIGS). Among his fields of interest include earthquake studies. He wrote a French dissertation on the central segment of the Philippine Fault System.