At 12:11 a.m. on Aug. 17, 1976, a powerful earthquake triggered the Philippines’ deadliest tsunami, causing widespread devastation across Southern Mindanao.

According to the Philippine Institute of Volcanology and Seismology (Phivolcs), the magnitude 8.1 earthquake, known as the strongest in the country since 1968, originated from the Cotabato Trench beneath the Moro Gulf.

The tremor reached its highest intensity of VII (destructive) in Sultan Kudarat, Cotabato City, Zamboanga City, Maguindanao, and other parts of Southern Mindanao.

Within just two to five minutes after the initial shaking, a massive tsunami surged ashore, with waves as high as nine meters devastating coastal towns such as Lebak in Sultan Kudarat.

The major cause of the high number of casualties could be attributed to the fact that the tremor occurred just after midnight, when most people were sleeping, and the tsunami struck from multiple directions, catching residents unaware.

Phivolcs said the tsunami affected over 700 kilometers of coastline along the Moro Gulf and the North Celebes Sea.

The disaster claimed an estimated 8,000 lives, injured more than 10,000 people, and left nearly 90,000 homeless, making it one of the most catastrophic natural disasters in Philippine history.

In Cotabato City, the earthquake and tsunami caused widespread damage.

Key infrastructure, including the Quirino Bridge and Tamontaka Bridge, sustained structural damages, while 14 buildings were partially damaged in Zamboanga City.

As Mindanao marks the 49th anniversary of the Moro Gulf earthquake and tsunami, the event and its impact continue to be remembered.

To help reduce risks from similar events in the future, Phivolcs advises the public to watch for three natural warning signs of a possible local tsunami:

* Shake — a strong or prolonged earthquake felt near the coast

* Drop — a sudden and unusual receding or rise of sea water

* Roar — an abnormal loud sound coming from the ocean

When these signs occur, people in coastal areas should evacuate immediately to higher ground, even before official warnings are issued, as tsunami waves can arrive within minutes.

Phivolcs said the Philippines is vulnerable to tsunami due to the presence of offshore faults and trenches such as Manila Trench, Negros Trench, Sulu Trench, Cotabato Trench, Philippine Trench, and East Luzon Trough.

Tsunamis in the country are rare but could be devastating.