The Philippine Institute of Volcanology and Seismology (Phivolcs) recorded the strong earthquake, which was initially measured as a 7.1 magnitude earthquake, at around 11:39 a.m. on Saturday. Its epicenter was located at 162 kilometers southeast of Governor Generoso, Davao Oriental.

It was tectonic in origin, which is caused by ground shaking primarily due to the sudden movement in the earth’s plates.

The earthquake was measured at a depth of 49 kilometers thus the strong shaking. Phivolcs said aftershocks are expected to occur.

The tremor was felt at Intensity 5 in Governor Generoso, Davao Oriental; Glan, Sarangani; and Koronadal City.

Meanwhile, it was felt as an Intensity 4 earthquake in General Santos City; Tupi, South Cotabato; Alabel, Sarangani; Kiamba, Sarangani;
Mati City and Manay, Davao Oriental; and Davao City

Intensity 3 was felt in Makilala, North Cotabato; Valencia City and Manolo Fortich, Bukidnon and Cagayan De Oro City; Maitum, Sarangani; Tagum City; Mabini, Compostela Valley; and Tacloban City and Palo, Leyte.

It was felt at Intensity 2 in Kadingilan and Don Carlos, Bukidnon; Tagoloan and El Salvador City, Misamis Oriental; M’lang, North Cotabato; and Surallah, South Cotabato; and Intensity 1 in Zamboanga City.

Around Saturday noon, the United States-based Pacific Tsunami Warning Center issued a tsunami warning as “hazardous tsunami waves from the 7.1-magnitude earthquake are possible along the coasts of Indonesia and the Philippines.”

Phivolcs said “minor sea level disturbances such as strong currents and rapid rise and fall of seawaters are expected.”

It advised the public to be on alert for unusual waves. People were also advised to stay away from the beach and not to go to the coast fronting Philippine Sea of the following provinces: Compostela Valley, Davao del Norte, Davao del Sur, Davao Oriental, Davao City, Sarangani, South Cotabato, Agusan del Norte, Agusan del Sur, Surigao del Norte, and Surigao del Sur.

People whose houses are located very near the coastline of these provinces were further advised to move farther inland.

The Office of Civil Defense in Region 11 advised coastal municipalities and barangays to implement precautionary measures. It also ordered the close monitoring of the areas.

“Owners of boats in harbors, estuaries or shallow coastal water of the concerned provinces should secure their boats and move away from the waterfront. Boats already at sea during this period (12 p.m. to 2 p.m., Saturday) should stay offshore in deep waters until further advised,” Phivolcs said.

Based on the tsunami wave models and early tide gauge records of the tsunami in the Philippine Sea, Phivolcs said coastal areas in the provinces fronting the Pacific Ocean are likely to experience wave heights of up to one meter above the normal tide levels.

“The first tsunami waves will arrive between 12 p.m. and 2 p.m., Saturday and may not be the largest. These waves may continue for hours,” Phivolcs said.

Cancellation of tsunami advisory

Phivolcs has cancelled the tsunami advisory around 3 p.m. Saturday as tide level has returned to “normal” height.

Around 12 p.m. Saturday, Phivolcs issued a tsunami advisory following the 7.2-magnitude earthquake in Davao Oriental.

Its monitoring station in Mati, Davao Oriental recorded a “minor wave” measuring 0.08-meter off the Philippine Sea, two hours after the strong earthquake struck Mindanao.

“The last recorded wave occurred at 1:10 p.m. for this station. Records show that wave heights have returned to the normal tide level,” Phivolcs said.

“With this, any effects due to minor sea level disturbances have largely passed,” it said, and “has now cancelled recommendations prescribed in our tsunami advisory.”

Ellalyn De Vera-Ruiz, Zea Capistrano, Antonio Colina IV, and Ali Macabalang