West Valley Fault

On July 16, 1990, a magnitude 7.8 earthquake struck the island of Luzon, causing widespread devastation and loss of life.

This came to be called The Great Luzon Earthquake of 1990, also known as the Luzon earthquake or Baguio earthquake and has been considered to be one of the most powerful earthquakes to hit the Philippines in the 20th century¹.

Here are some key facts about this seismic event:

Epicenter: The earthquake’s epicenter was located in the town of Rizal, Nueva Ecija, in the northern Philippines. However, its effects were felt across a large part of Luzon, with the worst hit being the cities of Baguio, Cabanatuan in Nueva Ecija, and Dagupan in Pangasinan.

Destructive Force: The earthquake resulted in significant destruction, including the collapse of buildings, bridges, and infrastructure.

Several buildings in Baguio City suffered extensive damage notably the Hyatt Terraces Plaza, Nevada Hotel, Baguio Hilltop Hotel, Baguio Park Hotel, and FRB Hotel. They were reduced to rubble with a lot of people buried alive.

In Cabanatuan City, Nueva Ecija a six-story concrete school building Christian College of the Philippines collapsed during the earthquake. It occurred during school hours.

The Philippine Institute of Volcanology and Seismology (Phivolcs) recorded “hundreds of thousands” of landslides throughout Northen and Central Luzon². The area believed to have been affected by landslides occurred in an area of 10,000 square kilometer³. Many roads were blocked, and bridges damaged or collapsed, making rescue and relief efforts challenging.

Liquefaction on the other hand involved an area of over 1,500 square kilometers³. About 100,000 houses were damaged.

Casualties: The Great Luzon Earthquake claimed the lives of approximately 2,412 people, with thousands more injured⁴. About 1.25 million people were affected³. It left a lasting impact on the affected communities.

Aftershocks: Aftershocks continued to rattle the region for weeks after the main quake, further adding to the fear and instability in the affected areas. A paper presented at the Tenth World Conference in 1994 on Earthquake Engineering by a certain R.L. Sharpe of Cupertino, California placed the number of aftershocks at approximately 700 times⁵.

Economic Impact: The economic cost of the earthquake was substantial, with damage estimated at around US$369 million. Damage to agriculture was pegged at US$57 million and damage to industry, commerce mining and tourism at US$148 million³.

Damage to the environment, however, is not economically quantifiable such as the destruction of the topsoil and natural vegetation. Dams incurred several negative effects, such as cracks and numerous landslides within the catchment basin. Electricity production was greatly hampered due to the nearly complete siltation of the Ambuklao reservoir. Irrigation activities were also affected due to this.

Awakening of Mount Pinatubo: Interestingly, the Great Luzon Earthquake was followed by a series of eruptions of Mount Pinatubo, a nearby volcano, in 1991⁶. An article published on Climate Policy Watcher, deduced that this earthquake must have somehow started a series of events that allowed the magma to rise beneath the volcano.

They based it on some accounts from some local villagers known as the Aetas who lived on the volcano of some activity on the mountain, including low rumbling sounds and landslides near the summit with steams erupting from the fissures following the earthquake in Nueva Ecija. Some scientists believe that the earthquake may have triggered these eruptions.

Lessons Learned: The earthquake prompted the Philippines to reassess its preparedness for such natural disasters and led to improvements in building codes and disaster management procedures.

The Great Luzon Earthquake of 1990 serves as a reminder of the seismic vulnerability of the Philippines and the importance of disaster preparedness in a region prone to earthquakes and volcanic activity.

Source:
¹The Asian Affairs
²Phivolcs: 1990 July 16 Ms7.8 Luzon Earthquake
³UN Office for Disaster Risk Reduction
⁴International Code Council
⁵Earthquake Engineering: Tenth World Congress
⁶Climate Policy Watcher